I just thought of an interesting process of Existence. Assuming that, if a dimension gets advanced enough, it is possible to discover true dimensional travel, then over the many long aeons, surely there must have been many dimensions to discover Existence, certainly more than how many exist now. So I considered this for a while, wondering about reasons, and then I realised: heat death. The imminent destruction of a universe would surely cause all of its residents to leave that universe or die out altogether, if they haven't already moved and blended with the rest of the population of aware Existence. So the number of aware universes would be continually kept down, and of course Tier 5 would keep some universes from discovering dimensional travel, as well.