
I'm one of the people that personally believe that the ONLY reason Midway Mania has such crazy lines at MGM is because when you think about it, It is the only attraction (besides GMR which many people skip because it's now hidden behind the BAH or they feel it's too dated... or the stripped carcus of the Backstage Tour), which younger kids can really ride.
The Rest of the park is shows, or attractions which have a much higher thrill level and height requirement which makes them unsuitable for younger kids or the ride adverse.
The park has a major lack of true Family rides (on top of it's general lack of rides) which is why the one 'popular' and 'modern' family ride in the park gets hammered with Fastpass runners and long lines thruout the day. DCA has a lot more options, even before it's recent re-do, for a family to enjoy together which has always helped keep it's TSMM lines shorter than the florida version.