I think the Borlas don't sell well because they need the proprietary Borla X-, which comes only in a no-cats version.
Think about it: Off-road compared to off-road, the stainless Borla combination is only $135 more than the mild steel BBK that's chromed on the outside (the BBK headers, not their bare steel X-).
I paid $320 something for my BBK ceramic shorties and $220 something for my BBK catless x pipe (from headers back). So around $550/shipped for both. Thats a lot of savings, plus I got 2 performance mods (that matter) for less then the stainless BBK LT by themselves.
No doubt stainless is nicer and last longer. Just a lot of coin to come up with up front.