Taking books from the carts makes publishers think they are making placements and doing something worth continuing with.
Not a recommendation because it wouldn't be a kind thing to do, but if these 90 books were rendered useless and then sent to the congregation they came from and identified as having been obtained from their literature cart, it might make a statement but it would also serve to feed their persecution complex and make them feel extra virtuous.
Having their very existence ignored, would be harder for them to take than actual opposition. As far as I can see, people are staying away from these carts, in droves. This literature cart thing might just fizzle out on it's own. Letting time take it's course rather than resorting to these kinds of destructive measures ourselves, keeps us from actually becoming what they believe we already are.