But there are dedicated rally and dedicated NASCAR games that do it all better, and far more comprehensively. What's the point of half-assing them in GT5 when there are other core parts of the game that could have benefited from the resources? It's like drag racing in Forza: half-assed and pointless because of it.
..because people still enjoy it? I occasionally race GT5 NASCAR/WRC/Kart, but I wouldn't buy a dedicated game. It's nice having everything in one game because I like a little of everything.