Might be coincidental the pax figures dropping off in relation to on time performance of American Airlines at MAN in the last couple of years. I know i for one has avoided MAN-ORD (taxying for 2 hours+) and to some extent MAN-PHL (ball ache to transfer) in the last couple of years because of this reason and opting for LHR or ATL instead to get to my destination.
Presumably many others have come to the same conclusion also.