Which doesn't answer the question of "why didn't they just double the clock without reducing the bus width" but your answer to the original question sums that up nicely.

Well, you could just increase the clock, but it doesn't really gain you anything. G.Skill already has the F4-4800C18D-16GTRS which runs at 4800Mhz. Is it fast? Not really. The F4-3800C14D-16GTZN running at 3800Mhz is actually faster in practice because you're limited by the memory module's latency.

Increasing the clock just makes it a lot harder for motherboard and CPU manufacturers to support those speeds, but on its own it doesn't really gain you a lot of speed.