Like what Purdie and others eluded to. Music Industry, period. The popular acts are groomed to make the biz money. They don't have to be able to sing, or dance, or anything really other than be what some study says will make the biz money. Once this is found, the biz will electronically make them sound good singing, and put them through boot camp until they can dance good enough to throw onstage to start making them money. They are much like Greg Brady was to the Johnny Bravo gig, "they fit the suit, man!"
Cookie cutter songs, same layouts, 4 bar solos, etc. They know what the human brain/ear sees as acceptable/routine, and exploit this with band after band after band of the same thing in a slightly different package.
Also, as others have also eluded to, all the money is made by the labels and in-betweens, and the "real" musician's probably don't even try to "make it big" anymore. They just crank out big-time talent on a small scale media outlet like you tube or gas station CD sales. I buy those 5 dollar CD's often when travelling, and there are some good acts out there for sure! I liken this to pro sports. How many kids would try to make the league if they weren't being paid the high percentage of the league's bottom line, that the CBA calls for? The music industry has no CBA, so they can continue to exploit those who will let them do just that.
The real major issue that started this downhill slide was when Sorum replaced Adler,crying2-07 and then Axl and Slash couldn't be in the same room together any longer. Rock and roll has been on a slow decline ever since.......