I think that interest being offered would certainly drive demand upwards a bit would it not?

Yes, a little. It's just that buying at $3 risks $2. If you hold a whole year (with no price change), you earn an extra $0.09. It would take 20 years for the potential upside of interest to match the potential downside of price drop to the peg). I don't think anyone cares about this much (assuming they even know about it, which is often questionable as @blocktrades stated).