Increasing drain current, decreases common-mode level
That's simple:


Say Vout1 has increased by a little bit
The current in the left branch then increases as the result of the CM feedback loop
The Vsg of M9 is fixed
The drain current of M9 wants to increase
Due to channel-length modulation the Vsd,9 must increase, why?
By the same token, the Vsd of the transistor below M9 must increase
So Vout1 must decrease to allow for the change in the current
Decreasing Vout1 causes the drain current to decrease as well
A decreasing drain current works in reverse to what said above
It eventually rises Vout1 up to the value it was before the change was made
The CMFB used here doesn't constrain a certain value on CM voltage level though
The same holds for Vout2


That's how CMFB works..

Note that the kind of analysis we're doing here is large signal, so in large signal analysis Req1 and Req2 are not fixed resistors, so your KVL equations fail to interpret the correct change in CM voltage level because you're not considering the change in Req1 and Req2 as well. You don't even know in which way they change. So you can't predict what happens to CM voltage level based on unknown values of Req1 and Req2.