I had a general question about card numbers.

Say there are 3E9 people on Earth, each with 3 cards. That's around 10 digits right there. There's 1 digit for checksum. I imagine you'd want to leave space for least 1000 financial institutions around the world, so that's another 4 digits. Which means you can only have 100 transactions per person.

None of this takes into account the fact that the same people are issued way more than 3 card numbers either.

So my question is, how are we not close to running out of card numbers? How is this not even a problem yet?