It's too much routine. Too much auto pilot. Too many identical days and weeks which get compressed into nothing. Few new memories will be made. Your life will feel much shorter and uneventful.
Doing random blue collar part-time work (I currently work as a gardener) and working on interesting projects in my spare time works much better for me. I can think about my fun project during work, not think about my work when I'm off the clock.
It is profound that I'm not the only one who quit a day job because of this exact reason. This is a biological fact. Your brain compresses memories that are too similar down into the smallest size possible. The result is that a year can often feel like a week, with a few memorable weekends and absolutely nothing else.
This is utterly frightening, and can feel like you've hit the fast forward button on your life and are careening towards the end.
During university I honestly could never imagine myself working more than 20h a week. And this issue was really on my mind, it worried me, I really couldn't imagine how, but whenever I brought this up people always said "you'll get used to it".
Nearing the end of my study funding, I took a part-time job programming in an office. Two days, 16 hours per week for two months was enough to wreck me for nearly a decade now. I won't ever trust people that tell me I'll "get used to" anything ever again. I don't know how they do it, I guess I'm just a different species or something.
It worked in that I felt re-energised to tackle the main app again after that.
There are days though, that I cannot bear to even look at a computer screen at all, and those days, I take up my guitar or another activity to focus my passion on...
Or maybe you're just not that into working in tech, and you're only doing it because x,y,z circumstance 'pushed' you into it when you were younger.
There's nothing wrong with career change, doing something different with your life, if you feel like programming or startups or whatever might be making you miserable.