Maybe pay is decreasing because it's not decreasing, our demands as Americans have just gone up. Or it could also be that there are more factors involved than there were 30 years ago.

Today there are are more planes in use, more people flying, more costs per plane, more pilots needed, more pilots available, more training opportunities, a world economy, more competition, too much competition, too little competition, more regulations, insurance, more expectation, and public relations issues.

This is just a stab in the dark...