They might not still have the game source and/or knowledge on how to recompile the game. There are lots of technical reasons that it might be entirely unworkable to do that even if they wanted to.
(disclosure: work in video games at a big studio where I know for certain there are things we couldn't build again at this point without a ton of work)
Has that situation improved at all? I appreciate many shops still cowboy code their way across the finish line, but I would think that big publishers might put more effort into ensuring digital preservation for potential remakes/ports/whatever.
For example, it is not outrageous for me to believe that Microsoft/Sony/Nintendo would require source code/build pipelines/something for any release on their marketplace. Or do they just accept a binary from developers?
That being said, I could easily believe that even if you had the game source code, there could be many additional bespoke toolkits, widgets, 3rd party binary libraries, etc all of which have their own inscrutable compilation process.
I think microsoft gets away with only getting binaries because they have a handle on the APIs you have to use for their consoles, so they can maintain backwards compatibility with a little translation, some shims, and the go-ahead from the publisher.
Nintendo also has the advantage of other people writing emulators for their hardware that they can take advantage of years later, but only for first party stuff. (later ps2 game releases for the ps3 did something similar, with sony hiring a prominent emulator dev)
I have to assume it's either licensing issues with toolkits/middleware or apathy that stops the release process being "ship us a binary and a docker container that can build it".
They can always just release a version without the music. This is a 12-year-old game, though, so maybe the sales don't justify the effort?