Because you cant just bump the teams that are finishing tournaments. There are about a dozen teams that qualify to be bumped, but bumping a 5th of the division mid-season isn't right either.

TXR - 40-5
Air Performance - 46-10
Diamond Sports - 51-12
Oilers - 50-14
Baseball Washouts - 46-13
Maniacs/Most Hated - 51-22
Advocare/Proway Ext - 50-21
Mash - 19-3
Untouchables/Buzini - 27/-12

Its not that ONE team is winning every tournament, but that the division just so happens to be top heavy this year. 2 of those 9 teams could realistically compete in C with their current roster. They'll all be bumped and probably 5-6 of them will stay together and go play C then it will be other teams turn next year to be in the group of 8-10 at the top of the D division.