Ask HN: Why is the future of advertising on mobile?

I spend far more time surfing, researching, and buying on a laptop or desktop than I do on my cell phone or tablet. The only stuff I've purchased on a mobile device is media -- music, movies, and games. The main reasons why I don't buy more on my mobile devices are screen size and ease of use. Also, much of my mobile use is spent doing quick things. My attention span on my mobile devices is very short. To me, it seems like advertisers wouldn't like that. Perhaps I'm just not seeing something.