IMHO some Star Trek writers didn't know enough about history to avoid making big errors in their historical references. Thus there were already historical differences from our timeline hundreds and thousands of years ago. Thus Star Trek was already in an alternate universe hundreds and thousands of years ago.
Once two alternate universes diverge from each other they will tend to become more and more different from each other. It seems just about impossible for two different alternate universes to ever become identical again. Instead they should just keep on getting more and more different from each other forever.
But there are also many historical references in Star Trek that seem correct as far as I can tell. And it is not like all the correct historical references are far in the past and all the incorrect historical references are in the more recent past. That would be the case if all the correct historical references were from before the Star Trek universe diverged from our universe and all the incorrect historical references are from after the two universe diverged.
Instead the correct and incorrect historical references are mingled together over hundreds and thousands of years. Correct and incorrect historical references follow one after another in random order. Once two alternate universes diverge from each other they naturally become more and more different from each other. They will not naturally re converge to become more similar to each other.
But our universe and the alternate universe of Star Trek do seem to diverge and then converge, become different and then become similar or identical, over and over again for hundreds and thousands of years. Since that is not a natural process, something or someone is acting to make the two universes become more similar every time they naturally drift apart.
Thus it may be speculated that something or someone very powerful is acting to make the two alternate universes, and probably many others, have similar histories, making them all closer and closer to a chosen history.