Schroth: because racecar.
Seriously, they are one of the few manufacturers that do actual research into improving belts and related technology, have the lightest, strongest components, offer an incredible range of combinations (you can order exactly what you want in a belt system, combining parts from their varied lines), there is a DOT option, and they have a very wide range of tested attachment hardware, etc.
Of course, they do cost more, maybe even much more. But belts are a subject like helmets- I tend not to shop on price on those things, because the cost of failure is so high, and the overall incremental cost (expressed as a percentage of the overall car cost, or a visit to a rehab center for a month) is very low. I think this is a case where the added price does have an explanation, at least for most of it.
I haven't bought mine yet, but my SLC will have them.