Paying the full movement cost, especially on a lot of the more powerful locations, is just way too big of a tempo loss
Other creatures you control have Vigilance. Yeah yeah, I know there's a bunch of other stuff on his card, but it's dumb and overly complicated
Brood Keeper may very well have adopted them given some of the close ties between humans and dragons in Magic, and her flavor text makes it clear how much she loves her little beasties
You can do some fun stuff with this in Commander, like using Ashnods Altar to pay the equip cost and looping through Mitotic Slime or Wurmcoil Engine tokens until you swarm the board
This is a great card draw machine there, ditto the two mana tap to self-bounce one of your dorks to your hand to jumpstart your Whitemane Lion effects or trigger leaves play effects
Bolas citadel takes care of all those issues