These studios have profit margins in the multi-millions, they could afford a symbolic $100k donation. Instead they choose to push their developers through another crunch cycle.
But ConcernedApe uses Monogame for Stardew Valley, the studios don't use Monogame. Why would they donate?
They typically pay a lot more than $100k for Unreal and the likes or employees working on their in house engines.
Oh and these studios often lose money instead of having profit margins in the multi-million, see Ubisoft.