I'm not party to the FB post in question, but:

Defer had obvious and extremely useful applications and little to no lag time to try them, whereas training habits is inherently non-instantaneous.

Defer used social anxiety as an example (which I think many readers have experienced to one degree or another), whereas Notice is about ... red barn roofs?

Defer had a super-catchy title, and may have gotten more clicks in the first place.

As an aside, part of me hopes that Notice and Defer constitute some kind of A/B testing, and that Brienne is figuring out how to make Really Awesome Posts, and is going to do so :D