LCL gradually migrated from railroad - owned & operated docks ( $$$ ), to private - trucker operated ($), mostly by freight forwarders ( Clipper, Dart, Superior Fast Freight ), but also by that UPStart package company. FlexiVan might have done a better job of retaining railroad LCL, ( and maybe even Mail ??? ) IF more RR's had bought into it. Still, by the late 1960's the trucking industry grew as the Interstate Highway System was built out; rail couldn't compete on service ( in most markets ) or price. Many RR's found out that they " ... were losing a Dollar a ton - but making it up in VOLUME !!! " BTW - FlexiVan still exists as a major player in the Ocean Port container chassis business.
REA was a lost cause after all the passenger train - off's in the 1960's decimated their connecting services.