Reasons? 1) Equipment, 2) Expertise and knowledge of live recording techniques, 3) post production, and 4) budget. Most of these DVD releases are recording using recording trucks with so many number of tracks. After the performance, the tracks are mixed in a recording studio, and if need be, some parts re-recorded and fixed. Kaya dinig lahat, kasi, all musical elements are picked up by their corresponding mics, like that done in the recording studio. Final post prod is the mixing of the audio with the synched video, all done in the most professional manner, normally in a pro recording studio or a theater mix room). Now, unless these things are taken into account here, the quality of our local releases will never equal the foreign released ones.
FWIW