Does it really? I find it absolutely annoying, tbh. To answer your question, its because of an unrestricted muffler with resonance that produces sound that may be considered halfway between tinny and bassy. Without the resonance from the muffler, it is annoyingly loud and tinny.
On a completely unrelated note, I once put a 400cc GSXR silencer on my CG 125. Got quite a shock, it was absolutely silent and the low range torque improved a lot. Even at full throttle it barely made more sound than a CD 70.