Why are beys like Apollon G, Dark Effigy G,etc. so rare/expensive?

I’ve noticed that the Hasbro-exclusive beyblades released with spin gears during G-Revolution are exceptionally pricey and hard to come by? Is this for competitive reasons, supply problems during their release, etc.?
Limited distribution, supply was short-lived at best in some areas (non-existent in many) and underproduced.