Letterman and, for 13 weeks Chase, took Hall's best time slots.
Interesting, when Johnny Carson retired CBS hired David Letterman and Fox hired Chevy Chase. On almost 200 stations Hall's syndicated show was moved to a later time slot (less viewers/less advertising revenue) or removed all together.
Now, as several of you have mentioned there were other problems facing The Arsenio Hall Show at the end, but basically:
THE BIG BAD BOYS EVENTUALLY SQUEEZED HIM OUT.