This.
It's only speculation that MM doesn't want Thomas.
From MM's perspective, you can see why he might at least be hesitant.
Both Pete Carroll and especially now John Harbaugh parted ways with him
He sees this team as in real harmony right now. It's all lining up well on a paper, though if you could spot an area of weakness, it'd be safety.
Baltimore saw their team as contenders and did not want any chance of a lone player derailing things
So, I'm guessing McCarthy just wants be very comfortable with it, and may not quite be there yet. I'm sure he has spoken tot he other coaches.