You are giving most front end devs way too much credit. Most just use React because that's what they were taught and see it as an end rather than as a means to an end as if it is an accomplishment.

Computers have become faster while websites have become slower. You can go on a random webpage and usually see 100s of MBs of memory being used while we had computers in the 90s running 3D games with around 1/100 of that. LLMs have partly become popular because people don't want to enter the current wasteland of web pages who couldn't care less what framework you used and just want to get what they are looking for and to get out.

You will see people write things like "powered by React" as if React is doing any thing except running more JS. You are not getting any closer to the CPU or any of your hardware that actually runs your machine.

At best some of these front-end devs want to appear as if their job is far more complicated and sophisticated than it is.

Every software has become slower, not just websites