User blog comment:Miskos3/Fairy Tail 514: Dragon Seed, Review/@comment-30338537-20161213161220/@comment-9595671-20161215124322

If Irene made a method to remove the magic, it's possible this is also why 2nd Gen Slayers can't use the Dragon Force, when she removes the magic it takes something vital that the DF needs, or simply the fact the magic isn't originally their's makes them unable to access it.

This also explains why the Magic is called Dragon Slayer magic, ever since I noticed Igneel and the other slayers' Dragon parents use it, I've wondered why it wasn't just called Dragon magic. Irene pretty much coined the name and it stuck.