I'm sorry, you're correct. Indeed, the number of users does matter, because what's causing instability is mainly the small number of individuals (comparably to UPI). That's why it's an alternative. Look, you're making some valid points, but I don't see why not having both?
To be clear I'm in no way arguing against bitcoin. I am just trying to put myself in the shoes of the average person and trying to see why they would consider moving to this. Myself? Big supporter. I am admire the technological aspect itself. This isn't arguing why I don't want to use it. I'm just trying to think of if the adoption would work if convenience is such a big factor. Yes global nature of bitcoin is a thing that's something I pretty much don't see happening with UPI. Thats a valid point.