For Hydraulic brakes that is fairly common but for cable stuff it is not really sensible as their are so many different options maybe you might want them for a flat bar but someone else wants it for a road bike but they have small hands and the other person wants it for a moustache bar but has giant hands. I don't really love package deals because if that were the case I would be stuck with calipers I don't want from SRAM or levers I didn't want from Cane Creek and who knows what cables and housing but probably not Jagwire Pro or Elite kit. It makes sense for Hydro brakes as they are a complete system and it is a bit tougher to mix and match (though Shigura is semi-common and Hope makes some 4 pot road brakes in both Mineral and DOT).

I like my choices and don't find that ever to be a problem. If you don't know what to look for that is one thing but if you are particular at least to a point freedom of choice rather than having to resell parts I don't need, is a good thing.