Where did the idea that "hearing impaired" is more PC than "deaf" come from?

I’ve heard several times recently that the term “hearing impaired” is the PC term for “deaf”. Which seems weird to me, because the Deaf community rejects the term. That was the absolute first thing we learned in my ASL class – “hearing impaired” is offensive. So where does the idea that it’s less offensive come from? Are people just mixing it up, or was there a change awhile back that I don’t know about? What’s going on here?