If they buy there is no payments to send out, if someone else buys they send payments to someone.
But isn't this part of the major gripe here, is that the payouts are low after the fees? With a virtual miner they can literally pay you anything (within reason) they see fit. Oh... BTC/USD had a bad day... your multihashlet is now in the red... here's a satoshi to keep you warm and fuzzy... always profitable!
They don't have to have an inventory to keep on hand, so buying back doesn't do a thing for them.
I get your argument... but it doesn't make sense in the virtual miner world.