How come evolution never came up with the wheel and axle? |
Why should it?
Are you expecting evolution to devise every conceivable answer to every conceivable issue? Good enough is good enough for evolution. Compared to wheel-and-axle solutions a pair of limbs (or many multiple pairs) were, apparently, quite sufficient a body plan that no other structure proved to be as advantageous for those clades of organisms.
So the answer may be as simple as saying a wheel-and-axle never developed because a number of more than adequate solutions had already been put into use.
Edited by AZPaul3, : No reason given.