I am one of those guys who were "left behind".

I used to code in ASP and PHP back in the day, and that approach made a lot of sense. You'd have things that run on the server, and then those things throw out a website for the user to interact.
If there's a need for reactivity, use some JS, but basically it all goes back to the same server program.
I always found that this approach was good enough. You could do a lot, heck, I even wrote a browser game back in the day. Most importantly, it was simple, and it led to great web pages that would always work and could be used as such. No JS, no cookies? No issue, your code would just deal with it. A button was a button, and link was a link, and your browser did the rest. Text got sent as html, pictures were loaded or not depending on your preferences. Everything got faster and faster. This was years ago.

In the meantime, I stopped doing web dev.

Suddenly, in the last ten years or so, I noticed that websites became bad. The whole web just seemed to regress. Everything was JS, everything became single page, and if you didn't enable every single function in your browser, or if you pressed the "back" button, or reloaded the page - basically if you did not pretend that the website's UI was an actual native program - then everything breaks. News sites stopped loading text or images halfway through, buttons stopped working. Links were not clickable. Pictures would not show up. LOADING bars and circle-things appeared on websites that were already downloaded on my computer. Registration forms did not load default options, choice elements were empty. Once the page was loaded, everything was sloooooow. Scrolling became "different" and often laggy. Websites would load, then do something in the background to reload into garbled messes. Printing didn't work correctly. It's like Flash websites of my day (that everyone know were terrible and had very few good use cases) became the norm, but without Flash.

What happened to the internet? Why is everything garbage? Did all web developers die out?

I went back to make a simple website for myself. Reading tutorials, it was clear I had to use some framework. It was recommended to use JS, install some sort of server application and database, then a framework on top of that, and then something that runs in the user's browser. But everything was its own programming language, with no common denominator. You'd either need a PhD in JS and server development, or be happy to buy in to some framework that was usually not even very good.
I did not understand anymore how web development works. I did no longer understand how the websites came to my customer, what the server did, how and when it did it... and everything was hard, even though this should all be really simple. And what came out was just... bad.

I went back to using simple web dev tools if I need to, and thought "well my needs are just not so advanced". But given that most websites have become so terrible, I just can't help but feel it all went wrong.
Whoever thought up this frameworks and JS revolution was probably really smart, and there are probably some really good websites out there.

But I hate the internet now, and I don't understand web development anymore.
I'm not even that old.