> why our industry seems unique in our willingness to do unpaid work for giant corps.

Because it never starts that way. It scratches an itch, solves an interesting puzzle and people thank and praise the work. Deep down we all want to be useful, and it helps that it looks great on a résumé.

After it's established the big corps come along, but the feeling of community usefulness remains. It's also why so many devs burn themselves out, they don't want to disapoint.