Buckethead,
It's because you're in your mid-Thirties, and had your hip ticket torn up years ago. Let me cite an example of what you're complaining about, from Johnny Cash. In fact, I'll cite two.
1) On his live collaboration with Willie Nelson for VH-1's "Storytellers", Cash mentions that he stole the tune for "Don't Take Your Guns To Town" from an old Irish ballad, "Clancy Lowered The Boom," and later jokes that Kris Kristofferson always wanted to write a song called "Let's Get Together and Steal Each Other's Songs."
2) The Johnny Cash hit "Ballad of Barbara" steals its tune, whole, from the English Ballad "Barbara Allen." The words are totally different, but it's the same EXACT version of the tune, down to the tempo, that I have heard most often from Appalachian musicians.
Regrettable as it might be sometimes (I'm talking to YOU, Sean "P.Diddy Puffy Daddy" Combs), theft is the one constant in pop music through the ages.
The difference, I think, is that the recombinant tendencies of pop music are much more in the forefront than they used to be, since the radio drives the market. For about six months there, about half the hip-hop on the radio had Pakistani or Indian music samples (NYC taxi-driver music), because one hit had it, and so everybody else did. A parallel example from the golden age would be the time in the 1930s that a troop of Danish yodelers toured the American backcountry for months on end. They were a sensation. The net effect? The early second generation of country music was full of yodels. Still is, if you know where to look.
Also, don't confuse your distaste for excrescent pop music with the decline of music as a whole. You remember the '80s well because the market has worked its Darwinian magic, ensuring that most of what survived from the era was pretty good. You don't remember Calloway, Rick Astley, The First Coming Of Kylie Minogue, or Tiffany because they sucked at the outset, and once they disappeared from the radio, they were gone forever. Ditto the '90s. You don't hear Candlebox that much any more.
But you're getting the current stuff unfiltered, and it hurts, a lot. At the same time, there are a lot of high points in the mediocrity. In twenty years I will welcome Outkast, Ludacris, Nelly (Hot in Herre!!!!!), 50 Cent, Mary J. Blige, Christina Aguilera, and even Ashanti's stuff as produced by Irv Gotti back to my ears with great pleasure, as long as we can forget about Britney Spears, Limp Bizkit, and Staind.
I would recommend trying not to listen to Top 40 or Adult Contemporary formats. They will rot your brain. In fact the narrowing of radio formats is a symptom of the problem you describe, and I long for the day when you could hear two different-sounding songs back to back on the same station. Like so many other things, the marketing of radio has become so refined and the models so revenue-driven that there is no such thing as music for music's sake, with a few noble exceptions like WFUV in New York, WXPN in Philadelphia, KPIG in San Fran, and their ilk.
[moreover] But you're SO right about sex in the lyrics. It's the audial equivalent of Penthouse (which is RATHER more than I want to see). Insinuation, innuendo, and misdirection are sexy. Talking about fucking is crass. But I would recommend you revisit your old blues records and see if they are all as subtle as you think.