Aww, maybe we should control for the Mysterious Space Police culling thing, and then the results would diverge like preschoolers let out on a May day. Like, there's a Prime Prime Directive. The MSP didn't apprehend Nero (natch), and look what happened?!
...I'm making a fully general counterargument, aren't I?:)
Well, considering that it's a fictional universe, the reason why so many species have such similar technology levels is clear; it's more enjoyable to listen to stories about species who are close enough technologically that there's some narrative tension about who will win in a given contest. While you can tell stories about vastly more powerful empires (see, for example, Q) such stories are better taken in small doses; and Q never actually goes flat-out against the Federation, because if he does, the Federation will lose instantly and there will be no sto...
Here's another installment of rationality quotes. The usual rules apply: