Exactly. But they don't.
The problem is that what FB, Google are currently presenting as "aid" or "development" for underprivileged regions is 1) restricted to their own services and 2) likely to be shut down in the near future on their whim.
If they are serious about development, that's great, but it seems to me there are far less self-interested avenues for them to do so.
Meanwhile these zero-rate programs are just another attempt at re-defining The Internet to be what they have on offer, and probably end up getting in the way of more general availability of the web.