It is a public good, and it would be appropos if corporations would support it directly rather than work at cross-purposes to it.

If Amazon is going to sell public domain texts, then it would make sense to source them from PG, and fund some money from those sales to the non-profit, similarly, they could then funnel reports of typos to PG for review and correction (it was a bit of a struggle the last time I tried to get a text corrected, and the project founder/director actually stepped in on my behalf).