IIRC MIA has a new baggage system in the works but like everything else at MIA is running behind schedule on opening. The current system I don't think is capable of handling peak conditions when for example multiple wide bodies arrive.

At MIA, you have many South Americans taking large quantities of goods back home due to being so much cheaper here in the US. Its worth for example for my Brasilian friends to pay several hundred dollars in baggage fees to take back home electronics purchased here for family members.