Most people aren't complaining because it cost money or really the multiplayer update itself. Most people's issue from what I've seen is the fact that to play the update you have to buy the game for a second time, which sucks for people who already bought it on itch.io.
I can understand that but sometime itch doesn't support something and they cant add an update but I think if you like a game a lot its just nice to support them on steam as well.
Bad mindset. Some people simply just don't have the money to purchase a game a second time (even one as cheap as Buckshot Roulette). It's also unfair to kick sand in the faces of those who chose to support your early when the game had less features.
