They need to get it just right in popularity.
Too little, not enough profit and not sufficient amount of players online = minimal amounts of servers, which may not last long (in terms of years) or fees
Too much, nice pay checks and too many people online = bigger demand for more servers, in which case monthly fees may be needed to pay for these servers (and fund the Christmas party
)
Just Right = nice paycheck, no fees, popular and a nice bottle of bubbly!