You do realize the reason many big companies do such donations and charity sales is to get tax deductions, right? Not to mention all the other loopholes they find to avoid taxes.
Also them having "zero reasons" to do this is far from true. They have done similar promotions in the past, without any similar situation calling for it. Hell, I'm not sure if it still is that way after the revamp, but one of the big draws of the RAF system used to be a huge exp boost.
Even if you could defend that such an exp boost will not lead to an increase in subscriptions, it's still simply good PR for them.
Don't get me wrong, it's a very good thing and I don't have a doubt there are many passionate and charitable individuals working at Blizzard that genuinely care for the issues the company supposedly cares about, but as corporation charity doesn't really exist in the same way as we see it as individuals.
People need to stop humanizing and seeing corporations as their friends. They're not. They're money-making machines. You don't need to offer loyalty to a brand or corporation, just care about the developers and staff.