Sorry, but it has nothing to do with "7AM."
The early buses will arrive at a given resort stop at varying times all morning.
There's no possible way that all of the resort buses would show up at all stops at 7AM, then no more for 20-30 minutes.
The poster happened to be unlucky on that day.
However, like all things at WDW, if getting somewhere is important, it is better to show up far too early than
to arrive just line minute too late.