Deeper mathematics is meaningful to me for its beauty and the way it feels like arriving at some fundamental truth, for whatever value that can exist. Similar for deeper physics, it's very appealing to me to try to understand the world on some fundamental level, as much as we're capable. And I find it very satisfying solving a good math problem just on the cusp of my limits.
Then higher up the chain is chemistry, electronics, robotics, software. I love seeing how we can put these things together for practical or just fun purposes, and I love when I put something together and get to see the end result working and doing something fun or useful. Doing the little lab experiments in my physics classes in college, it was really cool seeing the math on paper describe what was going on right in front of me, that I made predictions for. Something more practical to put my skills to use a while ago was the light setup I made with turn signals and some other safety features with an Arduino for my ebike. Admittedly I also enjoy when someone sees what I did and appreciates it but I also do it for myself. Then there's AI which brings up all kinds of philosophical questions.
And on another plane I'm getting into the things that go along with homesteading like plant science and animal husbandry. Home grown food tastes better and it's another thing I just think is cool/fun.
This all comes from some combination of appreciation, awe, fun, practicality, or just finding things cool - not seeking validation or running away from something. But I can still heavily sympathize with wishing I had a hundred lives to live, or got to live a thousand years in some kind of university, so I could fully appreciate all of these things. Right now I'm getting out of a long depressive slump and feeling like I've wasted too much time letting myself go intellectually, and wishing I'd dived even deeper on some of them in the past, but I'm feeling good about the future now.