There should be some research about the influence of autopromote variables on participation, vandalism, editor retention, and such things.

I am mainly talking about $wgAutoConfirmAge and $wgAutoConfirmCount. You can see their current values in InitialiseSettings.php.

These are different in various languages, and they seem rather random to me. The idea behind autoconfirming is supposed to be to prevent vandalism without hurting wiki ideals and editor retention, but I don't think that we really know whether the current values achieve these goals. They seem to be based on the editors' intuition rather than data.

I went over all the bugs that are mentioned in the comments of InitialiseSettings.php. All of them say something like "we had a discussion and we reached a consensus". I cannot read all these languages, but my wild guess is that people just threw some numbers around and voted to accept them. The discussion in the English Wikipedia is, non-surprisingly, the longest (47 A4 pages); I didn't read it all, but it doesn't seem to be based on any metrics either.

Anecdotally, I can recall many more times when I, as a Wikipedian, had to explain people that they need to do a few more edits to get a permission to move pages, than the times that I had to revert bad page moves by new editors, so there is a possibility that the autopromote values are not actually helpful.