The marks are a direct descendent of Fender amps
This is the answer. The tone knobs (with treble pushed in, bass pulled out) are exactly the same as on a classic blackface/silverface Fender. Randall Smith (founder of Mesa Boogie) started out by modifying Fender amps. Then, when he made the the Mark I (simply known as the Boogie from Mesa), it was a souped-up Fender. The design of the tone knob circuitry followed Fender's design. Hence, the template for the whole rest of the Mark series was set.
Once Mesa started to increase the gain on the amps, they added the push and pull pots to modify the knob's EQ frequencies to make it friendlier for higher and higher gain, but the basic behavior was set from its Fender roots.
In British style amps (Marshall and derived amps such as Soldano and Mesa Rectifier), the early parts of the circuit (where the Mark series has its EQ knobs) are hard-wired to cut most of the bass and low-mids. Since pre-gain bass is bad, the relative lack of bass in Marshall-style amps made them sound too thin at low volumes, but made them sound awesome when turned up to the point of distortion. Hard rock!
By contrast, have you ever turned up the volume on a classic Fender amp (or reissue of a classic)? Have you ever turned it up to the point of getting a really distorted sound? On those classic-style amps, I think that it getting it to the point of heavy distortion makes it sounds really mushy and kinda bad. The primary cause for the mush and flab is that the guitar signal has too much bass, which makes the distortion get flatulent. It's the same kind of effect that you get with the lead channel on a Boogie if the bass knob is incorrectly turned up.
Guitars and guitar amps are full of historical "features" such as this. They're full of vestigial tailbones and appendices waiting to burst. If you're into circuits, they're fun to learn about.