> Plenty of the software I use on a daily basis is open source software where you could argue that the economics shouldn’t have been there.

Me too. But the problem with "the economics just aren't there" means that if I cannot get, just from word-of-mouth (say, a Show HN post) 100 users @ $10 once-off lifetime purchase, then this is not a product that is in demand anyway. An open-source/free product that is exactly the same would similarly receive no love from users.

IOW, if not enough users exist for this product at $10, not enough users exist for this product at $0. Your passion product will still result in the dev burning out on the fact that no one wants their passion enough.