Reading direction should be inverted: we should read pages bottom to top
If I could flip a switch and change this one aspect of modern life, I'd be willing to re-learn all my old reading/writing habits. It just makes more sense to "build" ideas upward.
It's top down for same reason things are generally left to righ. In the days of ink and paper, you'd end up with a smeared mess - ask a lefty what a pain in the ass that is.
Less of an issue nowadays of course. Still the very idea is a bit nails on a chalkboard to me, but I'm old and wondering if it's a generational thing. Maybe you feel like this since many interfaces push text entry to the bottom?
Less of an issue, for sure - but not gone entirely. As someone who takes a lot of "manual" notes with pen&paper, I would still regularily end up with a smeared mess and dirty arms by writing bottom-to-top.
Besides, I don't really see an advantage over writing top-to-bottom. Even the OP only states personal preference / aesthetics as a reason, but no practical use that would make it better than the current version.
A problem would be that when writing you'd end up with your arm covering what you've already written and you dont we that problem with the current standard.
Other than this I see no problem with it other than a change to a system that has been the same in many cultures for millenia.