Bullshit is much easier to learn and do when you are young. I am not sure why this is, but a shift does seem to be common once you start to hit your 30's.
This is why it is much easier to recruit people in their 20's to work super hard on problems that don't really matter in the grand scheme of things. Once people get older, they don't really want to spend all week optimizing a tiny button on an Android app that no one will ever see or use, no matter how much you get paid...
When I was young I didn't realize what I'm working is bullshit. I thought it's the coolest shit in the world. I used to be excited about new technologies. Now when I hear about "new technology" I just roll my eyes, because in %99.99 of the cases, this "new technology" is anything but. It's just a permutation of an existing tech with trivial differences that I'm interested in learning.
Maybe when you're starting out, this kind of work doesn't feel as much like bullshit because you don't have enough experience to differentiate. It feels like you're on your path to becoming a better engineer and the struggles ultimately seem worth it. But I bet once you hit a certain point, having to wrangle with the same flavor of bullshit you did 3, 5, 10+ years ago feels a lot more soul sucking. It doesn't feel like becoming a better engineer like it once did because, in OPs case, learning the syntax/structure of a new JS framework doesn't feel like the sort of vertical learning it once did. You probably want to learn new, more advanced concepts, not "I know how to do this in React - how do I do this in <new JS lib>?"
Similar to JimtheCoder, I think it is experience. As a fresh faced college grad, I got hired at a bank. They have good recruitment, and a decade ago, the entire company was almost cult-ish (in the least bad way possible). The mission was constantly talked about, our members are the most important, we are helping members - our neighbors and public servants - with their problems, and every employee works toward that mission.
It felt really important. And to some extent you can still feel that in some places, even that bank.
However, as you get more experience, and you see the same political mid-management games play out, and you realize a lot of the cynical realities of things, you can lose energy. Or, perhaps you watch people not doing the right thing, but having no power to convince them to do otherwise.
Like an old man telling a child that digging a hole with a shovel is better than digging it with a rock and watching them continue to use the rock: you just get worn out.
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I agree with the main reply, that burnout is a thing, but that yes, it does help to be working on something you care about if you're going to put the level of mental effort required in software/IT. Sometimes I dream about being a bartender. You do your job, deal with the shit, and go home.
This is why it is much easier to recruit people in their 20's to work super hard on problems that don't really matter in the grand scheme of things. Once people get older, they don't really want to spend all week optimizing a tiny button on an Android app that no one will ever see or use, no matter how much you get paid...