Why would Luna-Com advertise the heck out of itself if it has no competition on Earth? Adverts, esp. on expensive media, is very costly. (The snarky remarks Marcus made in response to the "Thank you for choosing Luna-Com" suggests there is no choice.) No competition means they can pretty much charge whatever the market will bear and advertising is of limited value.
Even when they have a monopoly or near-monopoly, they might find it useful to keep reminding people of their service, to increase usage. Kinda like the Western Union ads, suggesting to immigrants from third world countries to send money to their relatives back home...
Just look at Comcast. Practically zero competition across most of the country, yet their ads are everywhere: print, radio, buses, and tv. Even if a small-time ISP manages to pop up, their voice is drowned out.
It took me three days to read all of "Questionable Content"...