Working with China would give them Intel on radars and anti missile and drone technology and procedures. The small Gulf states don’t have craft with the needed technology and “legs.”. They would be a logistical burden and no help. Saudi Arabia is at war with the Houthis and would be in an offensive rather than defensive mode. Not the signal the coalition wants to send.
You realize we are “ defending” Saudi and Gulf oil shipping without Saudi and the Gulf, the Gulf of Oman without Oman, and Red Sea/Suez Canal shipping without Egypt?
But hey
We have Canada