Note this is my personal opinion.
I feel like original or non-licensed themes made by Lego are dying out, particularly action themes. In 2007 there was Aqua Raiders, Bionicle, Mars Mission, Exo-force, Factory, Racers, Castle. Now we’re left with Ninjago, Nexo Knights, Elves and Ideas to a degree (I decided Speed Champions doesn’t count because they’re modelling off licensed cars).
I was just wondering, what happened?
I think original themes are still successful as you still have the themes you listed above (and LEGO has said that these themes are making money)
But it’s a lot of work to make an original IP rather than adapt one and the licenced themes are very successful. I don’t think they’re dying (we have a Ninjago Movie coming up soon, not to mention the LEGO Movie Franchise), I just think LEGO is trying to focus on making successful themes rather than spread out across multiple themes.
Expanding from what @ToaKhrazix said, I think the reason why there seemed to be a lot more in the past was because each only lasted for a few years. Comparatively, Ninjago has stuck around for many years now; if Ninjago had been cancelled way back when, I’m sure another story theme would have risen in its place.
The ones you mentioned were niche themes, they lasted for two years at most (save Bionicle) and Lego has changed its policies on it’s own IPs and started having two+ IPs of it’s own and the time, and with Ninjago ending in 2020 we can see that one of the IPs lasts for 10 year (Bionicle is the first, NInjago the second) and a bunch of three year ones that fill in the other places (Chima, NK, Elves). Then there are the staple themes of Lego, like City (and to a lesser extent, Friends). But with all the hullabaloo around Star Wars right now, Lego has been putting more effort into that while really keeping focus on it’s own 10 year IP, Ninjago. A while after Ninjago ends, a new IP will most likely take its place until 2030. Final point, Lego is putting more effort into Star Wars because of how profitable it is, so they have and 10-year IP of their own so that they can still have original Lego themes, along with the smaller three year ones. It’s not that these original themes are dying out, it’s just that they last for longer now.
Wasn’t that Chima’s whole purpose?
Yeah, probably. Ninjago, though, has outlived Chima by quite a bit. 
About half of lego’s themes now are original themes. They are City, CMFs, Creator, Elves, Friends, Nexo Knights, Ninjago, and Technic. Of these, Nexo Knights, Ninjago, and arguably City are action themes targeted specifically to boys. So the question is, are original themes dying out? Original boys’ action themes are dying out, sure. But I think this is because lego is learning that these kinds of fantasy themes do not have the longevity that other themes have. Almost every kid that grew up with the first years of bionicle no longer cares about the line since they find it simplistic and childish, whereas something like technic is much more interesting, to engineers anyway.
You also have to take into account that we are living in an internet-dominated age that loves to advertise pop culture everywhere so naturally lego is trying to adapt by licensing out their products. Not saying it’s good or bad, but that’s what lego is doing to survive.
Personally I don’t care if a theme is licensed or not so long as it adds new or recolored parts to the element system. They could just sell me a blank cardboard box with sand blue armor in it and I’d buy it, as long as it’s priced competitively with Bricklink.
Do we know Ninjago is ending in 2020?
Going off of what you said, I do agree that our internet based society is part of the problem. I remember hearing an analogy once about bionicle. Why would a kid buy an action figure of a character lego made up that he/she has never heard of before, when he could buy one of his/her favorite Star Wars characters instead for a similar price? I don’t think many kids want unlicensed themes.
No, but there is a substantial increase of liscenced themes over the past 10 years.
Going off of what some people have said, I’d also say that LEGO is taking a quality over quantity approach, as most of their in-house themes normally get a show. They also have way too much going on as-is, and factory space for a bunch more lines would be a bit hard to come by.
That’s true that original Lego themes are running longer, except for Bionicle G2, Pirates, Castle. Lego still tries making new themes, but they often die out within a year or two, instead of reaching the traditional three year run. Nexo Knights is a possible exception. While Nexo Knights fulfills a new Castle sub theme, Pirates have died, though this year it might look like Pirates of the Caribbean might replace it. One other major sub theme, Space, has been extinct since Star Wars came back. Nothing original in Space since Galaxy Squad in 2013, probably because Star Wars is so much more popular, especially since new movies come out. Though there was a similar gap 2001-2007 when the Star Wars prequel movies came out.
To me at least, it looks like licensed themes may be replacing sub themes, at least temporarily if not permanent.
Such as? Chima, Friends, Ninjago, and probably Elves and Nexo Knights all ran for more than three years.
hes talking about 1 offs such as ultra agents, galaxy squad, space police 3, pirates 2015, etc.
The run for a year and thats it, sometimes they may get a wave 3 but they arnt meant to last very long
There is now also speculation and rumors of Nexo Knights is ending soon courtesy of a Brickset article, and there is a new topic related to said subject.
If this happens then the original story and action themes will be down to Ninjago and Elves, seeing as Lego Ideas has turned into another outlet for licensed sets. Not exactly a great outlook, especially to ten years ago, original themes nearly doubled licensed ones in number.
With each fail, in the eyes of Lego, they seem to become more discouraged and convinced that profit lies in the licensed themes.
Well to be completely honest Nexo knights wasn’t the best theme. A lot of the sets were pretty much clones of each other, so this doesn’t really surprise me. I think Lego’s problem with these non-licensed themes is that they are not very creative when it comes to sets. Except for ninjago and elves, which I believe is partially why those two themes are so popular.
You mean in terms of build or appearance?
Appearance. I mean they all have the same colors and everything.
Then I definitely agree with you, a bit more variety would have been better.
One thing I still can’t believe is that has in three years Ninjago is ending. Aside from Bionicle, Ninjago is my favorite line that uses bricks. It has introduced me into a new detail and I nerded over that show. And with the movie coming out, I think its safe to say that Ninjago is Lego’s most recent popular line. #thankYouNinjago