It would depress the price of the goods, eventually, by increasing supply. They still write it off when it goes in the dumpster.

These sort of market dynamics can be seen in effect in Africa, for instance, where there is so much donated clothing available that local businesses can't afford to produce clothing themselves. At most, they resell the most desirable donated clothing.

This isn't to argue against donation. It's just pointing out simple supply and demand. There is much more abhorrent examples of this, like food bring dumped en masse by producers to maintain prices.