Electric rock guitar has been explored fully in terms of “riffs”. That’s the reason you don’t see many more of them. People have figured it out already. The puzzle has been solved. Even when The Strokes briefly reinvigorated the guitar riff in a popular sense in the early 2000’s, it was “just” a reapplication of stylings that had already been done by people like Tom Petty, Lou Reed, and bands like The Cars.

The last meaningful pioneer/innovator of electric guitar sounds as employed in the context of rock music was Kevin Shields in 1991 on the shoegaze album Loveless - and even that was a far cry from being a matter of what we think of as “riffs”.

Guitar riffs could certainly rebound some time in the future as a popular presence in mainstream music, although I don’t suspect it will. Nor do I particularly care whether it does or doesn’t. If that does happen, it’s not going to be anything you haven’t heard before anyways.