I recently travelled all the way from Edinburgh to Manchester Airport on time all the way - only to stop about 500M from the Airport platform, where we waited for almost 20 minutes.
Perhaps your train stood outside in sympathy with some of the car jams that have built up as a result of the closure of the rail bridge on Outwood Lane
although after the "interesting" morning last Monday, things have been revised and I'm told the traffic is flowing more freely.
If that was in the last couple of weeks, it's probably because one platform is closed to facilitate the building of the fourth platform. Capacity at the station is always on a knife edge and one little thing causing delay knocks on very quickly. The number of services have been cut to meet this platform capacity restraint but the above still applies. The timetable should return to normal in the first week of April.