This may be a ridiculous question, but....

I read somewhere that the pro racers don't use a frame for long. A year maybe, and then it's replaced. Is that just because the frame sponsor wants them to ride the "latest and greatest" or is there a useful frame life issue?

If there is a frame life issue, then how many miles for Carbon, Ti, Steel, Al? What factors are involved, removing crashes from the variable list?

I'm just curious on this.
Thanks!