[gmueckl]

Your argument does not work from a technological and economic angle.

On the technical side, most game code is present in the final distributable as abstract MSIL, running inside a VM. So you wouldn't need the game source code to port a game in 99% of the cases.

Big budget titles use engines for which they have source code access. So studios can just go and update thesw titles whem they want and that is what they are doing. Small studios and indies don't have that luxury. They use Unity because it isncheap to get locked into that plarform and get the game out. If Unity ever goes under, there is simply no engine code that they can maintain. No indie can afford a Unity source license - it's multiple of their entire budget. They would have to recreate their games almost from scratch on a different engine if they ever want to re-release them. And the results will always be subtly different from the original. This is a fate that awaits about half of the games of the Steam catalog.