Serious answer: Bootstrap. That framework did more damage to web design than any other framework. Yeah, its nice that you can spin up a page in a second that looks like every other page on the internet, wait a minute... Technical answer: CSS It was a nice idea, and it sure beat hand-designing each and every page (wait a second, weren't/aren't we doing that all over again?). It did/does too much, and was mostly in lie…
Every SaaS under the sun, hell half the things here that end up with some sort of VC backing... the first thing they do is spin up a nothingburger landing page that says a whole lot of jack diddly squat that all have a familiar feel where everything's centered, there's meaningless bulletpoints and info cards, but no real meat or information that describes what you're after... that feeling = "how do i beat gd level 1 (this landing page) so i can find what im looking for" and yeah. This has bled into documentation spaces as well, somehow rendering documentation (the thing that is supposed to help you get oriented) feel like you can't actually find what you're looking for.
UX/UI in the past decade was blown way out of proportion and I can't help but feel like it's been shaped by way too many imperfect half theories / stupid market research and is way too heavily influenced by marketing and adspace to be taken seriously. In general there is certainly a taste for what makes a good UX and that to me is typically a blend of utility and looks-cool. But without any utility everything feels like a goddamn waste of time & I'm mostly assured that websites that sport pages like this have way too many financial strings attached driving their every move. They all try to drive you towards filling out a sales inquiry form. It's ironic and hilarious that a lot of times if I want to learn about some platform or product, the last place I can reliably go to is their own website. These days you just gotta go digging, ask claude to go collect a bunch of user feedback from around the net or something.