I really think we're actually talking about the same thing here, because I agree with most of what you said in your reply.
What I don't agree with is:
I don't think anyone here is living in any sort of denial, hoping that Bionicle is going to come back. I'm certainly not. Most of us, including myself, do have other interests (or a "new Bionicle" as you put it). For me it's art and character design. For you it's Transformers. Everyone has a multitude of different interests.
Where we disagree is that I don't believe people are buying LEGO in some vain effort to keep themselves into it, as in:
People buy merchandise of things they have an interest in. I'm sure there's an adult out there who still holds and interest/appreciation for Sesame Street and buys its merchandise. Now, he/she probably doesn't appreciate it for the same reasons as they did when they were young, but an adult could appreciate Sesame Street for the art of puppetry, the technology behind it, a love of children's entertainment, or various other things. And if they like it simply because they find it entertaining to watch, that's their own prerogative.
What I'm getting at is that I don't think anyone buys something to try and convince themselves they like it. It would be a waste of money to do so. People buy LEGO because they are, in fact, interested in LEGO. They buy Bionicle because they are interested in Bionicle. They buy Transformers because they are interested in Transformers. And at the same time, most of us also pursue our various other interests outside of those things.
Obviously for some of us, our interest in LEGO has dwindled. Mine has quite a bit, especially since Bionicle ended. But if I go out and buy a LEGO set, I do so because I'm interested in buying it. And I personally don't post about it because I don't find it that interesting or worth sharing.
I know I'm being nitpicky here, but there isn't really such thing as a "sub-franchise." All of those things you've just mentioned are indeed a part of the collective Transformers franchise. It's like asking someone when they say they're a Marvel fan if they mean the MCU or the comics. It's all the same brand.
Now, I realize some of those different versions are a lot less popular compared to others. I know the movies aren't loved very much by the Transformers community outside of a few. But that's not what I'm talking about, I'm not comparing different versions of the Transformers to each other. What I mean is that, collectively, those various different versions of the Transformers are, nowadays, a lot less popular than when Transformers was just G1, because nowadays kids are into Fortnite or whatever mostly. The Transformers brand as a whole, while still very popular, is no longer at its peak.
But it's a moot point because I now get what you were trying to say in your first post. It doesn't matter how modern or popular it is, if it's one of your interests, then that's fantastic. Pursue it as much as you like.