Brown has to really show himself on special teams units.
Where he would be slotted in the receiver depth chart wouldn’t provide him a lot of snaps in the offense. He’s very good at contested catches, doesn’t run the full route tree.
Those fade routes get people excited but that doesn’t mean he’s anything close to a complete receiver. I would wager good money the coaching staff probably sees Mingo as more capable of stepping in any taking over #3 duties (which is a big role) should someone go down than Brown which is what folks don’t understand.