budejovice: It was the Witcher Adventure Game. It phoned home when I installed (on launch day, they since tinkered with it) and I was using an inferior connection and it couldn't update Galaxy and the game couldn't be played. Left a pretty bad taste.
I remember that now, they did fix it though really quickly if I remember right. Mistakes happen, so I wouldn't hold it against Galaxy because of an annoying bug.
Anyone worried about that should note all Galaxy games that need it for multiplayer have a offline shortcut available that bypasses Galaxy completely so you don't have to grab the updates or whatever for single player. Stuff like that shouldn't happen if you use the offline/regular GOG shortcut.
budejovice: There are more reasons, that was just off the top of my head. I don't have internet at home by choice. I don't really want any clients in my life. The tax software my firm uses just went to a client and it's just a total shitstorm. I made one purchase on gamersgate, realized I needed their client to download, and never went back. Don't use Steam.
I may be persuaded one day, but everyone's going to have to do a lot of unpersuading first. :)
I get that, I don't generally care for them either... but Galaxy has been great for me and my GOG collection was getting out of hand. To many games to keep track of and updated.