Because while that's the top-line for the 18,000 people affected (12,500 today), he'd desperately like that not to be the only thing the other 100,000 people who are staying hear. He wants the rest of the people to first hear: "We're changing for the better, and while these layoffs are a bad thing, it's necessary pain we have to go through to be better in the long run." That means wrapping the bad news with as much context and transparency as you can, every time you talk about it.