In the '70's, I grew up in a small rural town that was dominated by Gibson guitars in local bands, and Gibson basses. I played trombone (and a bit of guitar and bass) in some of those bands. Cutting to the chase, the Gibsons seemed to play like guitars - often short scale, a nice feel, and huge sustain off the pickups with a fat but somewhat muddy sound (and yes, that bridge pickup on the EB-3 didn't really help all that much.) This worked well for many people at the time, but I think the main reason for differential popularity is that the Fenders generally have decay characteristics that work with drums far, far better than the sustain off of those Gibsons.
I really think its that simple. The Gibsons are cool for playing what amount to third guitar parts, but the Fenders have more of a drum-like punch and really help to create genuine groove.
Here's the kicker - show me a funk bassist that used/uses a Gibson.