Why is that a problem? Evolution does not say "oops, it's Tuesday, time to evolve to a different form."

And it is only trivially true in any case, as even a species under no pressure shows genetic drift. It may look the same to you (or to me, for that matter), but then most modern cars look alike to me as well. Get someone who knows the details, and they'll show you a long history of subtle but definite changes.