What do you mean? That guitar music isn't "charting" is not an indicator of anything, especially with streaming. It's not the 90s anymore. Rock isn't the music of youth since 20 years ago, but guitars still sell extremely well.
Polyphia is one of the big bands that are fully instrumental and also maintain the spirit of virtuosity (more aligned with metal than rock, but the guitar-centric piece is there). There are other amazing guitarists and artists in a fairly interconnected community such as Jason Richardson, Plini, ichika, covet, etc.
I would likely agree overall interest has waned as it's not as mainstream as it used to be. But I'm more inclined to say guitar-centric music seems to be going through more of a transformation to fit the mainstream or certain niches than sunsetting as GP said.
Unfortunately, it seems that all attempts at significantly improving on these nostalgia laden designs are doomed to be relegated to an "uncool" fringe.
As guitar oriented music seems to be sunsetting, I assume that these tired old designs will continue their dominance. As a guitar player who cares much more about ergonomic design and technical innovation than the trapped imagination of nostalgia, I hope for a new wave of guitar music and a guitar technology renaissance, but I doubt it.