I work for a retailer and have been loosely involved in a project like that a few years ago.

Basically, it felt like it was mostly a very inexpensive way for the company to get everyone involved feel like they were making a good action. The free advertising was definitely an argument to get the higher-ups on board, but my impression was that it was kinda secondary compared to the kinda fake good conscience it gave everyone.

There was definitely no tax breaks for that initiative though, so at least in my country that is indeed a myth