I love the Markbass Compressore. But I've never been wild about their amps unless it's Michael League who's playing through one.
But as far as Markbass's diminished popularity goes, I think it has more to do with evolving tastes rather than an actual issue with their products per se.
The bass world seems to oscillate between liking the fat and warmer classic tube sound and the so-called modern clean with fast transient response and punchy sound. A lot of which mirrors what's happening in terms of this year's most popular playing techniques. A slapper, tapper, or twenty notes a second Jaco fan will want a very different amp than a classic rocker who cut her teeth on the late 60s and early 70s music scene.
My whole critique of Markbass is it's not really an iconic sound - and it's expensive. There's plenty of modern amps with their own voice and feel (Mesa being one of several good ones) as well as plenty of classic amps that each have a unique sound since that's the way tube amps are.
Markbass just didn't bring enough of its
own to the party IMO. Nothing wrong with the amps. Just nothing special enough (as far as
my ears were concerned - YMMV) to make it worth the risk of wandering that far from the mainstream at those prices. I already do that enough with the basses I prefer to play.