I don't know if it is a good idea either but the fact is, sales taxes take a larger chunk of lower incomes than they do higher incomes.
Yes, I agree it's a regressive tax but from a consumer behavior point of view, it's better to have something tangible in your pocket than to save money on a purchase.
Even if lower income individuals would benefit more, that's not the way it would be perceived. Like Squid said, giving people that money would've gone further in both buying votes and in stimulating the economy.
I really don't understand what they were thinking.