I'm pretty sure Mastercard did know that there are a lot of CC companies that already use crypto. And they just want to get a share of that pie. And if they do it now, their share can still be enormous. If they just take the same percentage the use now for traditional payments, the will get a lot of exposure to crypto. And they might speculate that the whole sector will grow over the next X years. And just them onboarding, will make it more likely for this to happen.

I use a crypto backed cc since nearly 1 year. It's NOT that you are paying in crypto, you still have to convert the coins to a stable currency and the top up your card with it. There are cards that 'make it look' like you are paying in crypto. But the do the same thing in the background.