It takes time (as in, many days) to notify >100M people. We're working on it. The blog post and assorted spontaneous coverage, like Hacker News, is faster.
Even then, targeting the most affected ones (those on free plans with more than, say, 900 photos) first is, I assume, a much simpler job that might save you from a bit of a public scrutiny and give those people an extra jiffy or two to act.