4 moveslot syndrome, when a pokemon has so many good moves to choose from, to make it simple.
Altaria needs coverage, healing and ddance while espeon is solely used as a cmind sweeper and has no room for heal bell.
Gardevoir can afford to drop a move while stil being efficent, but even then it kinda limits it.
Heal bell can be useful to setup on chansey with some kind of healing move, but most of the times it's not gonna work.