Saying “I don’t drink (or eat sweets, or whatever) is easier than saying “I can’t drink (or eat sweets, or whatever).”
When it comes to sticking with avoiding something “I don’t…” is a better way of framing it than “I can’t…”
When there’s something you don’t do, it’s just that you don’t do it as opposed to can’t which implies it’s forbidden to do and so maybe it’s desirable and you need self-control.
For example here’s a simple way of eating to stay healthy with only three rules, and one exception.
Don’t eat sweets, snacks, or seconds – except, occasionally, on days starting with “S” (Saturday, Sunday, or Special holidays). Lots of words starting with “s.”
If you just say “I don’t eat sweets,” it’s easier to follow through with than saying “I can’t eat sweets.” It’s that you don’t eat sweets, not because you’re not allowed to eat them or because it’s forbidden.
I can’t sounds like it’s taboo. Being a taboo makes something more attractive in a way, mainly just because it is taboo.
Saying I don’t becomes something I don’t do, I could do it, but I don’t. I don’t drive without a seatbelt on, I don’t go shopping on Black Friday, and I don’t zumba.