It's a pricing problem. To begin with, $25 probably isn't enough to make the project financially successful, as it can't be expected to sell in large volume. Small-volume products need to find a sweet spot in the demand*unit-price curve. If no such spot exists, as may well be the case for software development tools, the developer may as well give it away. The Mac market is particularly low-cost, low-return.

Secondly, if the product were priced at a point where it produced a viable revenue stream - for example, Logic Pro X addresses a very large market and is priced at $199.99 - one could hardly expect the student discounted price for the full product to be less than $25. However, my experience has been that no matter how low-priced the product (greater than $0), students will always ask for a lower price. :)

It's sold through the Mac App Store only right now, so it's limited to what the Mac App Store allows, unfortunately.

Maybe in the future, if it goes well, the developer might consider selling outside the Mac App Store, and this have more flexibility. I have no knowledge of his plans on that matte,r though.