Namechanger I don't understand why people with good incomes have credit cards. I think some of those people are going to become unstuck if Brexit ends up being a disaster
Like you we don't have a mortgage, we own our house, we have a very good joint income, we don't need any credit, but having a credit card makes buying things a lot easier, and gives protection more than a debit card can. Last year we went to USA, family of four adults, the payment to travel company - for flights, car hire and some hotels - was huge, had they gone bust before we flew, then we would quite possibly have lost the holiday, whereas by paying with CC, we had protection.
We pay the bill off every month, we have significant savings so will never come unstuck, regardless of Brexit!!
if they saved most of what they earned they wouldn't need debt for anything
We save most of what we earn - have no debt - but that doesn't mean we don't find credit cards an easy way to pay for things.
We have encouraged our DS to also have a credit card, so that when he finishes uni he will find it easier to rent a house or ultimately buy (he has an inheritance so will be in the position to buy a lot sooner than most). He is very sensible, using it for 1 or 2 small transactions per month, with a DD to pay off the full amount.
As for credit files, well there seems to be plenty of people on MN who can't rent or buy because of a poor credit rating, so it seems it does count.
Used sensibly, credit cards are fine.