If I was in GSP's position I probably wouldn't tweet either.
Between training, press conferences, interviews, charity work, family and whatever else he does I'd be using my free time for myself.
For people like Dana, Arial and other reporters its part of their job to use social media to promote.
GSP doesn't have to promote himself, he's in a position where he can afford to pay people to take care of the little things like social media, housework and yes... mowing the lawn.
Lets be honest, the reason most of use social media is because 1: we enjoy it and 2: we have the time. If you haven't much time and don't enjoy it, why do it?