This works by replacing assets, config files or even by injecting binaries into pre-compiled games, as well.
Minecraft is in a pre-compiled language (Java), but so is Skyrim (C, C++) which is famously modded (although most mods are written in Papyrus which is an interpreted scripting language, the game itself wasn't).
Most mods for Tekken (C++) also work this way; they simply replace assets and config files.
I don't think I've seen games do that, not even to advertise other games from the same publisher/developer. But then, the only five games I've played with a launcher are three MMOs, Genshin, and Honkai Star Rail.
Sometimes updates require a game to be restarted. With a launcher it never needs to REstart, it will be started fresh afterwards anyway.
I've noticed Genshin Impact on Android (which doesn't have a launcher) regularly needs to restart after updates, while the Windows version (which does have a launcher) never requires in-game updates nor restarts.
It's also in general a good place to centralise account management (esp. if parts of the game would need to be reloaded if another account is logged in!)
Lastly, although this is more of a side-effect, but it gives a good place to shows recent news/posts of the company about their game to players, such as when there'll be downtime, in a way that's practically impossible for the players to miss.
Oh man thanks for reminding me AG exists! They're amazing!