For many people, getting a large return at the end of the year makes more sense as they do not have the ability to save money. While it's true they aren't earning any interest, with rates well below 1% (A few online savings accounts do slightly better), these people are looking at, what saving $100 - 150 over the course of the year? The cost of the interest free loan is rather inconsquential under many scenarios and I'd argue that people are actually better off, not worse off due to the forced savings. For many, it's the only savings they have.
Furthermore, for those with refundable credits, there is no way to get those throughout the year. Some take advantage of the Advanced Earned Income Credit to fix this, but still. There is a lot of value in this forced savings mechanism. Some of you act like every one out there is perfectly rational.