We're going on complete and total conjecture and personal experience here, because I can't find any data...
DigiTech seems to have risen, almost entirely, from the ashes of DOD, which was essentially the sub-Boss budget company making stompboxes of varying quality with extremely unreliable switches. It seems like all of the worst qualities of DOD have wandered over to the incredibly crappy Rolls/RFX group, while DigiTech took off after their flagship Whammy Pedal made them a household name.
Now DigiTech seems to have consumed DOD entirely, re-releasing the old DOD pedals in new enclosures (with reliable switches) and are a worthy competitor to the overrated Boss stompboxes. Like every other effects maker at their level, DigiTech is competing in the multi-effects and modeling market and are holding up well: they've put out their fair share of classics, and Michelle is currently using a DigiTech vocal processor on stage as an indispensable part of Ubik's sound.