As platforms evolve, old games become unplayable. Open sourcing them will help us preserve them for future generations.
A lot of old games have become unplayable on modern hardware and operating systems. I wrote an article about how making games open source will keep them playable far into the future.
I also discuss how making games open source could be beneficial to developers and companies.
Feedback and constructive criticism are most welcome, and in keeping with the open source spirit, I will give you credit if I make any edits based on your feedback.
Not only do the games need to be opensource, but their toolchains too. It would also be great if everything were stored in content-addressable storage. Then it wouldn't be necessary to track down stuff by follow URL paths to dead domains.
I hope that opensource game engines become more popular. It might just be a matter of time. Blender is now very popular and that's opensource.