Aisle donkey chiming in here....

The carts didn't work for two reasons:

They were half carts that were very top heavy and prone to tipping over.

The passengers supposedly did not like the fact that when you had four carts in the aisle at one time, access to every lav was essentially blocked.

Based on conversations that I've had with fellow flight attendants during and since the half cart fiasco, many/most of us would love to use a full size cart like every other airline.