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.