[Squirrelloid]

Large maps lead to excess tediousness, which makes late game annoying *even when you're winning*.

They also tend to be large enough that large factions arise which are balanced in power and you get this endgame stalemate where no one can accomplish anything decisive. This doesn't tend to happen on reasonably sized maps (imo, ~12 players tops, no more than 180 provinces). (I have seen it happen in a 12 player game though, but its rarer, and it seems less likely the fewer players you have. I consider 8 players on 100-120 provinces to be ideal).

Finally, people get annoyed at the excessive unbalancing influence leavers have on the game, as this increases with size. On the one hand, a smaller fraction of the game's players border an early leaver, meaning the advantage gained by being next to a leaver is much more lopsided in favor of a small fraction of the players. On the other hand, the tedium and length of the game leads to more lategame leavers, which leads to rather boring 'grab the leavers stuff' gameplay, and tends to be to the advantage of turtlers since they are less likely to be in a war, and therefore have more free material to snag lands that are relatively undefended and for which no reprisal will be forthcoming. (non-turtling players ability to commit forces will be limited by the need to at least defend against the forces of those players they are at war with).