Yeah, I've have a few games that I've really enjoyed the bands from.

This is kind of diverging from the topic, but....one of my annoyances in video games is that that there are a number of video games that I play to the point of getting tired of the music, but don't have the option to buy more music tracks for. There are mods for Stellaris to add more music tracks -- people clearly want more music -- but even though Paradox is a game publisher that specializes in putting out games with huge amounts of DLC, they don't sell additional audio for the game, which just seems bizarre to me. I really wish that Fallout: New Vegas had commercial DLC radio packs in the same genre, but nope -- though there are people who have made enormous free "radio" mods for the Fallout series, like Old World Radio and Old World Radio 2 for Fallout 4, so there are clearly a considerable number of players who'd like more music to be available.

This doesn't work for games that you play through once and are done with, but I kind of wish that when a band creates audio for a game that one spends a lot of time playing, that the game developer would at least provide the option to buy more audio from the band for it, as long as it fits. The amount of developer time required to incorporate additional audio tracks seems very limited, and if the band is still producing audio in the same style, it seems like it'd be a sensible fit.

What's even odder is that it's become extremely common for game publishers on Steam to go the opposite direction and sell access to the game's soundtrack to play independently of the game. So they're basically acting as a music vendor already. That's also very low developer-effort. But they very rarely have DLC to add more audio from the band back into the game.

Cities: Skylines is the only game that I can think of off the top of my head where the game publisher sold additional DLC music.

I don't understand why either game publishers or music labels wouldn't love that kind of relationship. If you're a music label, have a bunch of IP, I'd think that getting royalties from your audio getting wider play is almost always worthwhile, and if it's in a game, it's not competing with non-game use; if anything, it probably promotes it. From a game publisher's standpoint, the cost to incorporate more music in many games is minimal, so the risk is very low. From a player's standpoint, it makes the game more-playable; the music doesn't wear on you.