Because that's where the seriously big money is. Internet means ads. And besides energy, food, labor, and shelter, transportation is one of the biggest necessities that humanity needs fulfilled to function. So yes. Covering the world in easily accessible high speed internet and inventing a new mode of transportation that cuts out the human factor (saving money again) are some of the biggest markets to make dough in. Also, Tesla's robot is aimed at disrupting the labor economy. Just imagine if tens of millions of people with menial (but too advanced for current "robots") jobs could be replaced by something that costs less than a car.

If you're wondering why big companies do the things they do: it's always money. Yes, Tesla may in fact help in massively reducing greenhouse gas emissions, but it just so happens that it's also profitable AF.