MRTC was a different concept from Economy Plus. MRTC was about improving the Y product across the board, and the cost had to be built into all Y fares. On the other hand, E+ is used primarily as a perk for elite UA fliers, and also as a cash generator (by selling upgrades to regular Y pax upon booking or check-in). Because E+ incentivizes frequent business travelers who pay higher-than-average fares, one could argue that it's worth the extra real estate.