Sometimes in pokerstars tournaments and also in Sunday Millions tournaments, players do not reach the guaranteed tournament prize pool
For example, to reach the guaranteed Sunday Million prize pool, a minimum of 10,000 players is needed, but sometimes there are as few as 9,600.
This means that the losses in the tournament in question amount to $4,000.
(yes they still get about 9600 dollars in rake profit from those 9600 players but that's another question )
If we talk about the Cardchat freerolls that pokerstars took away from us, then it's not nearly as big a loss for the pokerstars poker site.