It's more than that, though. "Reanimation" is an hour-long album full of remixes, many of which feature very obscure guest artists. It was released way back in 2002, whereupon it didn't sell as well as "Hybrid Theory" in 2000 or "Meteora" in 2003, and spawned no hit singles. Quite often, it doesn't get a mention at all in cursory overviews of the Linkin Park's history. A casual fan who doesn't really follow news about the band might be aware of "Reanimation"'s existence but any or all of those facts might prevent them from being open to checking it out. Even if they hear from someone or another that it isn't half-bad. Nowadays, if someone is interested in listening to "Reanimation" for the first time, I think that it's fair to say they're putting in more effort to dig into Linkin Park's music than a "casual fan" would.
Yeah, it was definitely a different world back in 2003/2004, when the "main" LP discography literally just consisted of Hybrid Theory, Reanimation, and Meteora. If you were a fan back then, you almost certainly had Reanimation, if for no other reason than LP having such a small variety of CDs you could actually find in a store. It's definitely been relegated to "obscure album status" over the years though.
They might be working on one. I've heard other people talking about a remixed album before, and on an LPTV video they played a never heard before Castle of Glass remix.
The label/band probably sent multi-tracks out to a lot of artists to remix. I bet they have a ton of remixes by those people we will probably never hear.