Several reasons for this, I think at least. The only time I ever hear of a good composer anymore is because of a sound track they wrote for some new hit movie. I never hear about composers on par with any of the big names from back then constructing master pieces, unless you consider Disney Movie Sound Tracks a master piece.
I wouldn't say that all music has digressed, because some music started out at low on the totem pole and saying it has digressed means it was actually good at some point in history. I'm not going to say what music I find revolting but it probably wouldn't be hard to figure out if ya'all seen my play list.
And how many people invest their money into Classical Music type CD's? The money just isn't in it to try and come up with the next Master Piece except too have your name recorded in history. Business supresses imagination to earn more money. If a business doesn't believe they'll make so much profit from your genre of music, then good-bye to you. No one is buying this type of music or cares anymore, so the businesses just follow the herd really, in a sense.
God Forbid music makes you think, too. How dare it even do such a revolting thing, as to make me think. I should get a lawyer and sue for just the thought of it. Now hand me my deep fried twinkies, I have to watch my TiVo recorded Maury shows and see if that really is her baby daddy.