Look at it this way. If someone were 'not' going to pay in full and just make minimum payments, which would mean a lot of interest for Amex, would they be interested in the credit card rewards? Amex makes money on those people and my guess is not everyone pays in full every month. I do now, but I've paid plenty of interest back when I couldn't afford to be paying interest. And I still went on vacation and used credit and points.
We have some smart, younger people here, but unfortunately they are not necessarily the norm, or we wouldn't have such a vast array of amazing and appetizing credit card offers. I'm happy to now be in this group but 20 years ago I was in the 'I have a balance' group.
And, I'm mature and can admit to my past shortcomings, but if you read the debt dumpers thread, which I do regularly, you will see lots of people trying to get through the period in their lives where they have energy to have lots of fun, but not loads of money to fund it and combined with 'living' costs, they've gone into debt and are trying to climb out. And they are on a Disney board planning trips at the same time.
Edited to add: last statement is not a judgement - it's a 'I can relate to this' statement.