Quoted from wikipedia:
Roots rock is just an extension of the rock, folk, country, and blues genres with an emphasis on live performance and genuine emotion.
If you read the rest of the Wiki article, the writers seem to think that the whole roots genre died in the 90s, even as they mention Tom Petty as the last of the great 'Heartland Rockers'. But I am here to tell you that the sound is alive and well. Maybe for the moment it's just fallen out of favor. For example, I was part of a scene in Los Angeles at the turn of the century that has put a few roots rockers onto the world map.
It's just that if the scene doesn't get support from the community, it starts feeling invisible. There are plenty of listeners, there are just no writers that are seeing the connections and putting out the narrative that some people still like the sound of an album that feels live. For me, it is just that those 4 roots - folk, rock, blues, and country - those are in my heart. I grew up on The Black Crowes, Crosby, Stills, and Nash, Johnny Cash, and Muddy Waters. You can't tell me that's not some timeless shit right there. And those are all very live, performance-oriented genres. So of course I still care about the live 'feel' of an album; that's a hallmark of the entire rock and roll tradition. I know there are a lot of people that feel just like me.
The last time roots rock was in the mainstream was in the 1990's. Well, by that measure, we are due for a resurgence in about 5 years. Bring it on.