Several reasons:
1. Lack of skills. Front-end has evolved from web design. If people like to criticize software engineering as “not real engineering” then front-end is the farthest thing from engineering that exists in software engineering.
One can see this in the programming languages, the code reuse (libraries, packages, etc), the tools and the attitude.
2. Too much ambition. At the same time I don’t think I’ve ever seen a community so driven by reaching their goals at any cost. Once apps kneecapped web sites the community had a major identity crisis which they solved not by doubling but by tripling down on HTML, CSS, JS and the like. Standards, common sense, performance, usability, privacy be damned. Because of point 1, the solutions they built were also just good enough to not completely fall apart. This is also why everything’s being rewritten in the web.
2. Too much money. Unfortunately companies like Google and Facebook made an immense amount of money ruining privacy for everyone and they could do this faster, better and out of sight with web apps.
They poured money into web technologies like their lives depended on it (because they did) and in the end managed to squeeze a round peg into a square hole: the fundamentally mediocre web managed to displace more worthy technologies and entrenched itself.
Every few years some poor soul realises the reality of their professional existence and writes a blog post or comment asking something along the lines of “Why is front-end so terrible?”. But there’s too much money in the status quo, so they either get gaslighted, or subtly dismissed and the cycle repeats anew.
And that reality is that you can polish a turd. With enough manpower, motivation and money you can really make it shine. But underneath, it still stinks and people will figure it out. :-)
Note: I got out of front-end in the 00s and then out of back-end a year later. Since then I’ve watched this never-ending train-wreck with amusement and amazement, but also sadness when realising how many real apps are replaced by soulless Electron shells.