because people love Dragon. You already know some people are currently excited about Alexandrite Dragon although a week later that card would be rarely used just like Megalosmasher X and Phantom Gryphon
It turns a wingbeat of giant dragon into a harpies feather duster, use the effect to summon, use WGD to destroy their spells and traps and then just special summon it again
Reactor needs 2 monsters to tribute summon and Maximus cannot be normal summoned. Vice Dragon has superior defense to all other lv5 2000 attack monsters I know.