It hasn't and it's all about architecture. Very few airports have the space, design and are willing to meet the cost requirements associated with creating a secure transit zone for luggage, the credentialing for employees with access and associated logistics issues. MIA and IAH are very dependent on TPAC / TATL to Latin America and the the space and money considerations are more than made up for by the efficiency (shorter connection time). Other than Canada (where intl. feature would only matter on the ORD-Canada segment because of pre-clearance on the inbound) would be interesting to know the volume of intl-intl. connections at other large intl. hubs such as JFK, IAD, ORD, SFO, LAX.