The main reason all of those champs are ban is simple, they dominate early game, and at low elo's people feed them early game and once they are fed, there is no "falling off" or coming back. You will lose every team fight.
*Note this low Elo*
shaco - early ganks, people forget to play passively and get taken out early, gets fed, destroys everyone
Morgana - High burst damage, with great sustain, mid gets caught with a snare + aoe + ult, easy kills, will destroy your team in a team fight
Shen - He is shen. High damage, high survivability, great initiations, Dat ult, and the taunt + jungler gank is nasty.
Kassadin - I've seen nearly every at low elo's who has gone mid, die to him, and then he 2 shots your entire team
WW - Gets a kill here and there, and suddenly begins to snowball due to players not understanding how to deal with a WW, either in lane or ganks.
Rammus - Ad carry is mad scared of him. (although i don't tend to see that many rammus bans)
Just my opinion as why each are banned, and i agree with these bans at low elo, except i'd swap rammus for olaf or shyvanna, i hate them so much lol.