Cause it will run out and there is no way to produce more, unless long periods of time are involved.

Helium on earth was produced over billions of years by decay of elements, such as uranium.

Earth-helium's final destination is space, it just sticks around places like natural gas wells, then canisters, then party balloons, etc. But one way or the other Helium will end up in space. That's cool.

It being very very finite makes it pretty cool, too.