Many nonbelievers appear reluctant to espouse the narrower, stronger version of atheism. Their basic view is simply that there is no evidence for the existence of God and therefore no reason to believe. Now, it's fine if they want to argue only for this weaker claim; it puts the onus of proof squarely on the theist (which is probably why the move is so popular). Nevertheless, there are good reasons for returning to the traditional, narrower meaning of the word.
For one thing, a broader definition is a less specific one, which means that it contains less information. If someone says they are an atheist in the broad sense, it remains unclear whether they merely lack belief or positively disbelieve, as both positions fall under the scope of the definition. The new usage has also led to the introduction of new terms, like “positive atheism” and “weak atheism,” which often cause confusion since different people mean different things by them. And anyway there already is a word for the broader concept: nontheism (a word that, incidentally, has much less stigma associated with it).
But more important than any of the above is that there isn’t merely lack of evidence for gods, just as there isn’t merely lack of evidence for leprechauns or for Russell’s teapot; there are reasons for positively disbelieving in all of these things. And why shouldn’t those reasons be part of the discussion between believers and nonbelievers?
This is why, when I describe myself as an atheist, I mean that I believe there is no God. And I wish more atheists would say that.