Equestria is, or was, known to be protected by the Elements of Harmony. They were created by the Tree of Harmony. There are, however, more than one Tree. There are even more than one Tree for every timeline. There are more than one of each timeline for each alternate universe that seems to spine off into such variations where Harmony was constructed as something other than a tree. Perhaps a pillar, a ring, or even a rose... With virtually unlimited possibilities, it's impossible to know for sure what iteration some hapless soul may be subject judgment to, if not their invitation.

For the Stranded Seven, they crossed the Trixie Bridge into a world of Equestria where there was a Tree of Harmony... However, this was not the world of Equestria they would have expected, nor were they such guests Harmony would have anticipated.