Exactly what says on tin.
No one like disadvantages on attacks. No one like to waste actions reloading. Yes, they deal more damage than bows, but bows have better range.
Crossbows used to be the reserve weapon for wizards. Now they have basic at-will spells to cast offensivelly. Just like battleaxe/longsword, the diferentiation of bow/crossbow should be more a matter of taste than bad mechanics.