Because there was almost no volume from 9.5-9.3, so you clear a...

Because there was almost no volume from 9.5-9.3, so you clear a few lines if nobody else decides to sell at 9.4-9 etc

Not to mention constantly changing prices you lose priority, so lets say you're selling at 9, you see 9.5 on the bid, you move to match that volume at 9.5, someone else decides to sell that volume at 9.2, they will get priority to sell before you. They clearly had a large line of stock to move (potentially could be instructed to do today) therefore they cant just tell a client, sorry mate i couldnt clear your stock because i f*ed around for a few extra dollars you didnt ask me for and we lost priority so only cleared half