They rolled in tanks at Temin Square because this is appenning around the country; I don't think they have enough tanks to roll into every city at the same time. They could start at one end and move but folks will see what they are doing and resist including disabling the tanks, jam a helmet or rock into the gears. This size of protest has not been seen in China since prior to WW2.
Things are changing but observation must be done. Putting skin into the game as Saudi steps up to be the monitor.