Almost everyone of a certain level of means has multiple cards. If you only associate with people around your economic level, it is easy to believe that everyone has multiple cards. I have many friends in NYC with only a single debit card and either no credit cards (due to no or poor credit) or a few credit cards that are all maxed out.

It's also worth noting that many companies with subscription services specifically block signing up with gift cards. I do not know if this would apply to Google Pay or not.