@gamingonlinux There are a couple of driving motivations I can think of, some technical and some business.

Business is for marketing and publisher/distributor links.

Technical is that it can serve as a “boot loader” stage to check integrity of game files (which may also be done by platforms like steam, but you may also distribute on other channels besides steam). The decoupling of the launcher binary from the actual game binary is probably an overall win for reliability.