A few potential obstacles:

1. Use of proprietary third party libraries. Havok seems to cost money for example. I’m not sure how Havok would work out in an open source model, but there are probably many other third party libraries that would stand in the way as well.
2. Distribution of assets. The game is not much without its assets, and many of the assets can be third party. For example Quixel Megascans. Even old games like Super Mario 64 heavily used third party textures and sounds. Not sure how they would like their assets be distributed freely.
3. Music. If the game uses licensed music this is a no go. It’s even difficult for companies themselves to release their old games with their original music.