How come it seems like most people didn't hear it?
Because it came out on a bullshyt low-budget indie label (TVT/Blunt Recordings). Flush is one of my favorite MCs, but he's never been one of those rappers hungry for the limelight. He got put on via his Mic Geronimo and Irv Gotti associations. But he's still putting out dope material. He dropped that posthumous collabo album with Sean Price (R.I.P!!) last year.
Flush songs getting the beat snatched and reused for other rappers seems to be a recurring theme in this man's career. Pete Rock reused "Questions" that Royal Flush recorded for Pete's album and let Raekwon use it for "Sonny's Missing" off of OB4CL 2.
Buckwild reused the intro track from Ghetto Millionaire, "I Been Gettin' So Much $", for O.C. on "Burn Me Slow" for his "Still Diggin' EP".
And I first heard the sample for Monica's "So Gone" off an unreleased track from Flush called "Section 8". He was also one of the first, if not the first person I heard rap over Gil-Scot Heron's "Angel Dust" sample on an unreleased track he did with Mic Geronimo.
*edit* Also forgot that Chinx Drugs and French Montana used the beat/sample for "Worldwide" from Flush on "I'm a Coke Boy".
Having a bigger name artist rap over a track you originally recorded can make or break an artist's career (See Ras Kass and Jadakiss "Home Sweet Home/We Gon Make It for reference).