But at the same time, he's looking out for Robin. What can Robin do? Not a whole lot. And Much doesn't know Robin is thinking of leaving (if he even is by this point), and would certainly not want Robin to leave. He is, in a way, trying to get Robin to see the bigger picture.

Agreed. I don't think there's any need for Much to apologize. He was trying to cheer Robin up the only way he could think of, not being deliberately cruel like Robin.