There is a finite supply of numbers. Not recycling old numbers and just throwing them in a hole forever wouldn't be very prudent.
There is an infinite supply of numbers. You can just add extra digits. Mobile phone numbers used to be 8 digits in NZ, then became 9 digits when they needed more numbers.
Numbers aren't limited to the amount you can count, there will always be more.
What did you expect was going to happen?
I'd expect it to be reused _eventually_; not right away though.