It ain’t necessarily so. Some of the services, ie the performer, caterer, printer, may be donated or provided at a reduced price.
Charities use this vehicle because it works. It gets attention, and many people open their hearts, and their wallets, when they are being wined, dined, and entertained.
If you are questioning whether your ticket price is considered tzedaka for the purposes of calculating maaser, or a charitable tax deduction, check with your lor (local orthodox rabbi) or accountant. Often a fund-raising dinner will indicate that the value of the dinner is $$$, with the balance considered a charitable contribution.