They don't make up the full 5% though, and there are people who do consistently use these cards only for their 5% categories.
I used to do this in the UK brought my monthly season ticket using a 3% cashback used to make just under £20 a month.
Of course the badly implemented EU changes which in theory should have benefited the consumer did not - the merchants just took the reduction in interchange fees and didn't cut prices at all for the end consumers
https://squareup.com/guides/credit-card-processing-fees-and-...
"The card that’s used
Debit cards with PINs are lower risk than credit cards, so they typically have a lower interchange rate. And rewards cards (travel, triple points, etc.) and business cards typically have have higher interchange rates."