Why arn't Annie, Cassiopeia, Leona and Galio banned too?

Annie is squishy and reasonably easy to counter in lane, Cass is very high skillcap, Leona is easily counterpicked and does no damage, and Galio has no easy way in and needs to be fed to do damage.

Because they have initiation tools to go with them besides flash, do lots of damage and are very tanky. Also can dive carries well.

because amumu and malph are tanks

Annie/Cass have some skill required in their stuns (and RNG, in Cass's case).

Galio tends to have his broken by a stiff breeze.

mumu and malph have the ability to shut down a carry. Malphites ASPD slow makes your adc useless, while amumu has really scary ganks.

galio isnt very mobile and his ult, while very good on paper.. is countered by life steal and tenacity (with enough range and tenacity u can walk out of it receiving 0 dmg)

Unkillable and with ****ton of CC. Hmmmm

Galio is very niche and much better against magic heavy teams which don't exist anymore. Leona is good cc but her ult isn't 1/4th the size of Amumu's. and cass and Annie have nowhere near the durability of Amumu or Malphite. You focus them they explode.

Because Annie and Cassiopeia don't jump into the middle of your team, smack around your carry and refuse to die.