For GPUs it could work as you say (except that the incentive for development of expensive and risky technologies would be gone), but I think that wouldn't help

For GPUs it could work as you say (except that the incentive for development of expensive and risky technologies would be gone), but I think that wouldn't help that much with things like websites. Most of the value of Facebook is in the network effect. Messenger has more than 1B users and I don't think it's a good app, Telegram is much better IMO (and is also used by almost 1B people in some countries - network effect there), and all Telegram apps are open source - well, backend isn't, but at least you can have modified clones (communicating with Telegram servers) with different features etc. And there is a small open source server implementation made by someone.