For small purchases bitcoin is not very convenient. Perhaps in the future it can be used in almost all areas, but for a glass this is not entirely convenient
It is not just about being inconvenient
Anyway, you can always order a Bitcoin payment card and pay with your bitcoins just as easily as you would pay with dollars (or whatever). It just doesn't make a lot of sense to spend precious coins on trivial things when you can spend fiat ("bad" money). I guess many people here apart from bitcoins are earning regular income in their local currencies, therefore spending fiat seems to be a preferred way of buying small things, all the while keeping bitcoins and earning additional income via Bitcoin appreciation