They will be playing with themselves if they do that. Maybe if a dev of a certain altcoin contacts them to manipulate order books and add fake transactions, they will do it for money. Otherwise, doing all of those stuffs will just be a waste of time and effort because at the end of the day, they are not going to earn any money at all.
I don't know that for sure, just pure thinking. Maybe there are some stuffs like this happening but it's just that it's not a good way for exchange sites admins to spend their time.
Exchanges have no other choice than to add fake orders to make the spread between buy and ask as small as possible.
If they don't do it, then the gap between certain price levels will be too big, where even a tiny executed sell order in potential can get the price to drop with 1% or so.
They want to attract traders with well stacked order books, so yes, they will continue doing so.