When I push myself to do these things, it loses all meaning. I do fun programming because it's fun, when I tried pushing myself like this virtually always I ended up more tired (for a miryad of reasons). And if I need to push myself, I'd rather just learn more Japanese, or do some exercise, or something else. But when I have like 1-2 weeks holiday, I will for sure sneak a few full coding days in there, and that is liberating.

I agree with this. But there‘s a big difference between building a habit of doing some intellectual or creative activity regularly and pushing yourself to do a specific thing.

Before having built a more regular habit I was often in a sort of excitement-burnout loop. That doesn’t work well for me.