Games under $5 are easy impulse buys and never regretted or refunded unless they don't actually run on my system. $10 would make me question "do I really want to buy this game?", which more often than not is a "no" or "not now", and so it just becomes another slot on the wishlist to be scrolled past and added when it's on sale.
At the same time 2.5 times less buyer is the revenues
At the same time if you want to validate a new idea, you want to know how many people say yes to “do i really want it” and not how many people impulse buy.