I'm not a pilot, but I have some thoughts on why KDEN would be better than KAPA.
South Metro is an excellent department has a great crash rescue response, but DFD provides a much greater amount of crash resources available. I think that at this current time, South Metro only has 2 dedicated ARFF units (Red 1 & 2) and 1 ARFF Engine (Engine 44). Red 1 is South Metro's only full sized ARFF unit and I believe that only the personnel stationed at Station 35 and Station 44 get a large amount of ARFF training. Outside of that, the resources responding to Centennial would be likely regular engine companies from other stations. Denver has 7 full sized ARFF crash units (among others support units) with all personnel on duty that are constantly trained on ARFF and a Chief who also specializes in ARFF. Just looking at the difference in number of emergency resources would make DIA a very appealing place in the event of an emergency (better safe than sorry).
As for other reasons, Centennial's longest runway is 17L/35R (10,000 ft) while DIA's longest runway is 16R/34L (16,000 ft). The plane landed on 34L, so they ended up having more than a mile of safety margin to land and slow the plane.