[Tijdreiziger]

There is a finite supply of numbers. Not recycling old numbers and just throwing them in a hole forever wouldn't be very prudent.

[toomanybeersies]

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.

[cbluth]

Numbers aren't limited to the amount you can count, there will always be more.