That is what they are doing. The theory is that once they put someone through being arrested, that person will not continue coming to protests the following days.
I’m am certainly not agreeing with the tactic, but that is why they are doing it.
They say to never attribute to malice what you can attribute to stupidity, but I just really don't know which way to go on this one.
NYPD is a lot of things, but stupid is not one of them. They know all the tricks and are not afraid of the ethical implications of them.