[amiga386]

1. For the most part[*], publishers on Steam use DRM, from kernel-level DRM which can crash and pwn your computer, to Valve's relatively lukewarm Steamworks., whereas GOG primarily (exclusively?) sells DRM-free games.

There are lots of ideological and practical concerns with DRM, I won't list them here other than to say game players want to be in control of their machines and their experience, not let game publishers control their machines.

2. Steam policy is that you can only run the very latest release of a game (it will update when you go online, and you can't remain offline forever). It takes away your choice to reject publishers bad updates - for example, when 2K forcibly added their marketplace/launcher malware to Bioshock games, breaking them on Linux, Steam was their henchman/goon forcing it on everyone.

[*] Not everbody! https://www.pcgamingwiki.com/wiki/The_big_list_of_DRM-free_g...