[piltdownman]

Workflow and accessibility. Not to be reductive about it, but they're basically a massively reduced barrier to entry for tasting what 'real' production is like for the less musically inclined consumer.

Grooveboxes are essentially clip-launchers; they were basically incepted as a sort of sample-less Akai MPC utilising a built-in ROMpler and some basic Synthesis, some FX, and 'contemporary' presets to lure in people fiddling around in music stores - e.g. the MC-303 or to take it to its absurd conclusion, the DJ-XII.

The interactivity thereafter is about launching clips on the fly and fiddling with the resonance and cut-off for a lead sequence, and riding that master FX ping-pong delay like your life depended on it. The Dunning-Kruger DAW if you will.