Problem is that to this point none of the wrestlers that Jones has fought has been able to consistently take him down let alone keep him down. Brock is stronger but if Jones has a reach advantage he'll definitely use it and as mentioned earlier Brock doesn't like getting hit.
It's 80-84 with reach, not nearly as much as an advantage as Jones is accustomed to. And brock is lightening quick with his takedown. Shit, brock was able to take Cain down twice.