The Spice Girls were always going to be a trend. As soon as they lost the novelty to their young adult fans and their little girl fans grew up they were finished. Then they'd have to wait for nostalgia to come back, which they did a few years ago. What was supposed to happen with them was one would emerge as the star people wanted to still see ala Justin Timberlake, Harry Styles, Robbie Williams, etc. But they weren't talented enough to stand on their own.
Oasis was a trend too, as it didn't matter what came next they weren't going to be the phenomenon they were in 1996. But rock bands always have more longevity than pop acts, as they can take the sales hit as long as it was a good record. But when they went around saying they're the 90s Beatles you can't stick to sounding like Help! forever and not make your Revolver. I know what the pop fans wanted, but the media really thought they were going to make something profound in the hype of 1997. So the attitude, especially in America where they were seemingly done overnight was "These guys talked all this shit about how nobody can touch them and they give us Magic Pie?" So they changed public opinion to "They blew it and The Verve and Radiohead got it right." MTV played D'You Know What I Mean? constantly and then ignored everything else, as Radiohead and Verve got the airplay. Even MTV News would be snarky about them.
But I guess the right thing would have been holding onto the b-sides and making that the third album, then taking time to do something fresh in 1999. I'm not saying they should have put out something that sounded like Aphex Twin with Liam singing over it. But a better version of Standing on the Shoulder of Giants would do. Nobody liked it because it was really morose (although a perfect come down companion piece to the coke binge Be Here Now really) But a happier band could have taken Noel's brief Beta Band fandom into something.
And here's the chapter in the Creation Records book I was talking about here.
The story is insane and the whole book My Magpie Eyes are Hungry For The Prize is great as it also talks about crazy Jesus and the Mary Chain stories, Primal Scream, Kevin Shields as a mad genius, and Alan McGee is a real character.