She announced her withdrawal, first to her teammates and coaches, and then to the public. Apologetic, regretful, wishing she could continue but unable to do so. We could wonder whether what she was saying was TRUE, but... we could not argue with the class and professionalism with which she said and did it.
Brown walked off in a huff. He refused coach's instructions in the game, made his decision and executed it without saying anything to anyone, in the most unprofessional and self-glorifying manner possible. You can even say that taking off the jersey and equipment was a thinly veiled insult to the whole Buccaneers organization. It was very personal, the way he left the field inviting a round of cheers for HIMSELF -- which of course did not materialize, as the fans had no clue what he was doing.
Simone Biles announced regretfully that she was mentally subpar.
Brown announced NOTHING, but DEMONSTRATED a mental health problem by acting out.
The issue between those two is not the difference in public reaction to their withdrawal from the game "based on who they are", which is to say identity. The difference is the MANNER of that withdrawal. The public reaction to it is completely normal, expected, even hoped for.
While we did not understand Simone's problem, we respected her enough to accept it.
HIS problem, nobody understands.