One day they'll realise that...
Less adverts means greater retention by the public.
If you only see one advert in a day, then you're pretty likely to remember it. If you see 100, then you'll most likely become poster blind.
At the moment there are to many people trying to advertise in every scrap and corner they can. By making advertising space a more common commodity they effectively devalue it as well as undermine their ultimate goal, public retention.
Now imagine Google auctioning off exclusive adverts on their mobiles. How much would you company pay for guaranteed retention?