It couldn't be a part of any legal settlement.
It's likely Paramount thought Colbert was potentially too much trouble relative to the profit he brought in. We likely had one too many talk shows fragmenting the late night legacy network audience with a similar format.
Time will tell if CBS comes back later with another talk show in the time slot.
I think CBS should put on a show similar to the old Sabado Gigante where some scantily clad Latinas parade around in sketches and dance numbers. I'd stay up to wait for that.