Modification isn't always about the difficulty. Sometimes it is (I've modified Monarch level to be a bit easier, but still clearly harder than Prince), but it can also be to change the flavour of the game.
On WB-fun: sometimes it's fun to play around with WB. Ever added 12 huts on your capitol's border so that when it gets the first border pop, they are all popped (and as they're popped by city borders, it's a completely safe pop)? Fun, although of course that'd make the game a lot easier.