They steal designs from other popular gear, lowering costs and defects since they're copying and not developing. Cheap parts and labor in china help as well.
Most of it admittedly sounds horrible, but there are some gems. I personally like the midi foot pedals and midi controllers as well as the headphone amps.
I wouldn't use mixers live but they're not bad for a rehearsal. Their 25 buck pedals are simply horrible. But sometimes they're so horrible that they work a la White Stripes and other similar bands who go for a super scratchy, dirty, raw sound. Anyway if you're on a tight budget, behringer's usually the first stop