Yeah, it's not about entitlement on any side, just simple conflict of interest. In most reasonable groups, everyone will be relatively close to center and willing to compromise.
But what happens if you've got a DM with a grand high-fantasy story plotted out, one player who wants to play his grimderp Mary Sue low-fantasy character with long emotional rants, another who's a massive munchkin and just wants to see how much he can kill, one who wants to play her Chaotic Evil backstabber to the hilt, and two who want to both RP and optimize a little bit with the end goal of 'kill things, grab loot'?
Or even something where the DM has a ton of material written out that orients around one specific area of the world with a fantastic overarching plot, but the party wants to go off to the opposite corner of the world and raid dungeons?
Obviously a good DM and good players would work together to make it as fun as possible for everyone (in that second example, it'd be pretty trivial for the DM -- if they're actually a good writer -- to let the players do what they want and link it back in to the plot, or for the players to figure out that the DM has something planned and try to loosely follow the tracks), but sadly not everyone is that willing to compromise; it's less noticeable online, I think, because there are plenty of greener pastures, which in and of itself discourages asshats from being as bad as they might otherwise be, since nobody is stuck with them as the only game in town.