[AdamC]

I'm not a FIRST expert, but I'm assuming it has to do with A) the very high price of renting out the venues for competitions (34 full-size stadiums for a complete weekend, plus the Georgia Dome and the accompanying convention center) really adds up. B) They have to have money for the FIRST scholarship that they give out to many students. C) FIRST has to pay the on-the-payroll workers who are part of the organization (ever seen FIRST HQ?).
Plus, they could always use a little extra bank to fund new regionals, expand other ones, and the various other things FIRST has to do. Sure, much of the cost of running FIRST is written off on the backs of large corporations, but FIRST must still pay a little of its own.