Chris Paul had a player option for this season that he could have declined to become a FA. Instead, he 'accepted' a trade to the Rockets. This allowed Paul to make more money than he otherwise could have and it also gave the Clippers back some quality assets. Basically, a win for all parties involved.
Irving was still under contract for two additional seasons. While I think his request is widely regarded as reasonable (for a trade request), the Cavs certainly weren't forced to trade him.