Why do none of the top houses do spring rush

Yes it’s that exactly. Honestly some more should there’s a bit of a stigma if your house does spring rush

Usually srats in the top 10-12 won’t do cob. Yet, any srat will only cob if they need numbers. This could be bc of people leaving after Fall or Dec graduation. Some srats will take a big # in fall bc so many graduated (or left after Spring) and then they usually don’t have to worry about spring. I was a gamma chi. I know AXO took 100 and ZTA had like 95. They wont need to cob. Also, many houses might only have 1 or 2 spots available. If so, they usually already have someone waiting on that spot. Those who cob usually need more to meet numbers. They need $$ from dues to pay for the srat house, nationals, etc

Are there really only 3 srats doing spring cob? Does it usually change?

ALL chapters will offer spring bids when they are under Total, but when a chapter only has a few spots open from December graduations, they don't have to go looking for pnm's and hold a 'rush'; they already know who they want and just offer the bids privately. Chapters don't have to make an announcement that they are offering COB, if they are eligible to take new members they need only notify panhellenic when someone has accepted their bid. This is why getting a spring bid is harder if you don't already know members in a chapter.

which 3 houses are doing spring rush?