From a team/parent perspective it would seem only right to refund the gate fees. From the park perspective that money has already been spent to prepare the fields, buy the field-dry, pay the mortgage, pay the concession and field workers, etc... The logistical nightmare of refunding those fees as you are walking out the park makes my head swim.
We seldom cancel a weekend tournament days ahead of time and the optimists among always think we can get the games in.
Most of these major parks with gate fees are not run by the tournament organizers and so they must conform to the park rules. In our tournament (we don't have gate fees) the expense of getting ready for the first pitch exceeds 30k. We even pay the umpires $100 each minimum even if they never saw a pitch just for being ready to go at our 8:00AM game and saving us that particular weekend.
No one makes out on a canceled tournament, not the park, not the sponsors, not the teams, not the parents and certainly not the players.