Nature isn't very smart and is very slow. For instance, a mutation that gives 10% fitness advantage (which is pretty much unheard of as far as I know) would only rise to fixation 20% of the time. And in humanity it would take 454 generations to fixate in the population. Since most mutations don't carry such large advantages by themselves, you have to wait for dependent mutations to take place. A second mutation might indeed give 10% advantage but only in the presence of some prior mutation having already fixated, which may itself only give 0.1% advantage.

There are a lot of low-hanging fruits nature has missed because nature only cares about how many copies of genes there are, it doesn't care about human goals. Evolution is a poor optimizer for what it does, it has no optimization for what we want done.