I would guess that the list is actually sorted most-pop to least-pop. So unless you get allies voting for each other, everyone just votes for themselves and the most-pop empire will always win.

Oh FFS another shallow development in the list of shallow developments in GCIII.

This, only the top 6 most populous empires are listed and are sorted A-F in descending order. With most of A-F voting for themselves you can see A usually have the lead and it comes down to the remaining factions that aren't included to tip the balance. Of course I've seen some odd behaviour where some AI don't actually vote for themselves but in most cases they do.