Venmo is far from ubiquitous. (None of my friends or family have a Venmo account, for instance. They prefer other apps like Square Cash / Google Pay / PayPal, or don’t use payment apps at all.)
Debit cards are not popular here because they tend to lack robust fraud protection - and even if they did, your bank account could easily be zeroed for weeks while they work to reverse the fraudulent charges.
Also, debit cards still have an interchange fee here. It’s cheaper than credit cards, but even for a small purchase there’s usually a $0.20 minimum fee - which is too much for microtransactions.