I suppose it's the nature of a more-or-less "closed" experience with a persisting fandom. In the eyes of the community, characters lose more and more nuance over time, makes it easier to meme.

For another SV example, I've been around long enough to see Demetrius move from someone who is ultimately loving but is at times overprotective of his daughter and has a complicated relationship with his stepson to someone who thinks women are incapable of doing anything and absolutely hates stepchildren.

It's definitely a problem in other fandoms too. Avatar and Undertale fandoms both do this especially. Katara from Avatar used to be a complex character that tackled all sorts of issues like having to be more mature than she probably wanted, dealing with complicated alliances, and, well, being a primary associate of the Avatar himself. But go over there now and look up Katara, you'll see the majority memeing about her being an emotional, nagging mess that won't shut up about her mom.

It's just something communities do eventually, especially ones where memeing is prevalent. It's like characters aren't allowed to be complex or flawed, lest their flaws become their entire personality.