The point of trading for Carmelo Anthony and taking Chris Paul on when he can walk at the end of the year is to GO FOR IT.
Trading off Capela when they basically have no other rim protection on the roster, on a pretty much capped out roster to boot, is not conducive to going for it.
There's no point in the Rockets going one step forward, then taking two steps back.
The Rockets can always look for other deals or wait to see if Melo gets bought out eventually. ( While that might not seem likely now, it still would be a better option than gutting their team of it's only true full time rim protector, and no Nene does not count here)
Nor are the Knicks getting an unprotected 1st rounder in any deal for Melo.
For the 10,000th time. If the Knicks ( or some other teams in a multiple team trade) are not willing to take Ryan Anderson, some non guaranteed contracts and a few protected/low picks, then it's no deal at all.
The Rockets can go on and function without Melo on their roster.
The Knicks cannot go on and function with Melo on their roster.
The PERSON WHO IS WILLING TO WALK AWAY FIRST IS THE PERSON WITH THE POWER IN ANY RELATIONSHIP DYNAMIC. If the Knicks don't want Anderson, then no dice, Rockets and Morey will walk from the trade table. The Knicks have far less incentive to walk from the table.