I'm a bit confused on what you're saying is different than that.
CoH stopped selling their product, they stopped supporting it. They have no intention of ever supporting it again. To release the source would involve no lost sales, as they do not intend to sell it again.
I absolutely say that while they intend on supporting the product in any way (even just maintenance mode), it's theirs, but once they stop using it completely and have no future intentions to ever again sell it, there's no harm in releasing it. Once the work is no longer being used by the artist, with the artist having no desire to ever use it again, why not release it?
Because people who might otherwise buy a new game, by the same people, would instead play the old one.
If you could somehow relive your favorite concert forever, rather than buy more tickets, artists would be devastated. I think their business rationale is totally sound: why not just sit on it, and people who want that same experience come to you for their new work?
Instead you'd have to pay a lot of money for lawyers and engineers to review the code, etc. That's expensive - it's not like they could just upload the whole thing to Github, no review, nothing.
Besides, the people who don't want to pay for a new game are people who you should spend zero time pleasing - they're not willing to support whatever endeavour you're embarking upon, so why spend all this time and effort putting something out there for them to enjoy? Sit on it: cost zero. Release it: Potentially costs lots, might decrease sales of current product.
It seems like a no-brainer from every perspective: as an artist, as a programmer, as a business person. I guess as a "digital artifact" it has some worth, but honestly, if it isn't enough to support the people making it, it really isn't actually worth that much (emotional attachment to games aside).
I wish, I'm sure they make a hell of a lot more than I do.
Many years ago I decided that keeping up with and being invested in games didn't make sense - stuff went microtrandaction, content released as add ons that clearly should have been part of the game, the focus is on multiplayer streamable, etc. I hate it.
So indy titles or GOG style games for me only. It cut way down on spending, toxic communities, supported artists and older digital works directly, and it's more fun (to me). Plus GOG games have no DRM!
You can't go around distributing OTHER peoples work, just to release your own. That's even worse!