Technically they don’t gain money no, but they get:

1. To move or dispose of product, making sales look better
2. Free marketing, both in people having the drinks and to say "look we did a charity"
3. To pay their taxes with effectively free money, because they take the product that they made for pennies, and count it as a “donation” at full price. Meaning that all the “profit” they would have made on markup goes straight to paying the taxes instead of making the money and paying taxes on the money they already made.

It’s why a company donating their product is always better for them than a regular person donating cash. They are effectively still making money it’s just this time they are making money specifically to pay off their taxes.