Blizzard says it's to remove clutter of spells that can instead be baked into one spell. I'm fifty-fifty on this. A lot of 'useless' abilities is usually what got the flavour to the class (Sentry Totem, Far Sight, Water Walking,) at least in my opinion.
I personally think Blizzard is trying to push the Esport scene slightly with World of Warcraft, making more simple spells and, less of them, with clearer visuals.
They denied it was to make it easier for newer players, to not confuse them, but I don't quite believe that myself.