It's mostly that people have objected (or simply pointed out, as a few have on this thread) that "cis" doesn't adequately describe their own experience of themselves, rather than that the term has been rejected outright. But I like your point (in the comment below) that "cis" and "trans" don't have to be binary opposites. They can be viewed as ends of a spectrum, with people positioned along it at various points. That offers a subtler model - but of course one that in no way undermines "trans" and "cis" as concepts, but rather depends upon them.