The most obvious group of people who avoid mobile phones are the elderly, and you can't just wait for them to die of old age because there will continue to be new elderly people avoiding mobile phones. At least until we solve age related physical deterioration. And waiting for the market to come to you isn't a brilliant strategy in any case, because your competitors are not standing still.

And as the OP states, it isn't just the people who avoid mobile phones who won't switch to tethered protocols, but people who want to message the people who avoid mobile phones. And a high proportion of us have elderly relatives, and we email or Skype or Facebook them.