What does the launcher do with regard to the operation of the game that cannot be done within the actual game itself? Is it due to a technical limitation or simply there for the convenience of the players? Are there alternatives to such methods of starting the execution of games?
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.