#3. They ARE Still Good, You Just Didn't Notice
It's human nature to see a narrative in everything -- all we care about is a good story, and the good story we most care about is the one we create in our own mind. This can predispose the way we enjoy art: If three identical artistic offerings are presented to you in three different ways, it's the most compelling context that will decide what you go for. Their new stuff might not be worse; the problem is that no second album can replicate that sensation of discovering a new artist for the first time. To put it another way, if one divides the story of a great artist's career into three sections, all of identical quality, you might find that they weren't actually better before -- maybe it's just their backstory that's boring now.
#2. Alternatively: They Sucked the Whole Time, You Just Didn't Notice
Or maybe they just sucked all along. Some artists can at first disguise their vast sucking, possibly through the audience assuming they are being clever/ironic when in fact they are not. How does this happen? Well, a simple lack of information can lead to some grotesque misconceptions. And then, when the full picture is revealed over the course of decades, it is often a cruel and shocking garden path that has you feeling nauseous and homicidal by the end.
#1. Making Good Stuff Is Really Hard
Making good shit is fucking hard -- that goes for airliners and oil rigs as much as it goes for music and paintings. That's why a world of billions of people has produced like five timeless sitcoms (and five good airliners), and why 90 percent of bands don't interest you, and why 90 percent of movies are forgotten forever three seconds after you're done with them, and why 90 percent of porn is just powerfully unsexy, probably. The good stuff is rare and special, which is why we like it to begin with.
That's why the new album sucks -- it's hard enough to be good once, let alone fucking forever. Sure, they'll eventually create a computer program that writes perfect pop songs, but it's gonna be boring as fuck (see the aforementioned bit about narrative). All humans are imperfect, so maybe those distant, wealthy superstars aren't so hard to relate to after all. Except for Bono -- he is a poison dwarf.
So don't jeer the one-hit wonders for what they didn't do -- cheer them for what they did, 'cause they've got one more hit than most of us will ever have.
Or you could just shut up and listen to metal.