At a guess I'd say because it's easier, there's a lot more know-how out there and it'll probably even be cheaper. And it'd probably go just as hard, if not harder...
I know of a certain Datsun that owes it's owner about 2/3 what my Corolla owes me, has about twice the power (est), has bigger brakes, is lighter and much much better setup than my Corolla. Has adjustable coilovers on all 4 corners, full harnesses, the lot...