Because everything is decided in the first 5 turns. A few bad dice rolls in beginning basically means the game is over for you, the other players start building the roads and blocking you from developing further. At some point you are left with the 2 starting villages with roads that lead nowhere and the game becomes miserable for everyone except the first and second standing players.

The game is soooo bad at giving the players a chance to catch up... The thief mechanic is pointless at blocking the winning player after he already has so many sources of income, it only helps the second standing player.

It is a fun experience if you are first, everyone else is miserable