His character was relentlessly cunty, bitter and negative in that JoBro show, and always looked on the verge of choking someone out. We know he can act and he likes attention, so what gives? Did he just not want to do it? (he sure took the money and the free global promotion for his band happily enough) There are entire episodes where he does nothing but grit teeth and snap at poor Kevin, who just wanted to keep it light for the kids watching Disney.
Nick also had really weird and obvious sexual tension with both his older brothers on that show, but that’s another thing.