There are some reasons why seo is considered to be better than ppc which i found on the internet(google):
1)It’s funner to buy traffic for cash rather than to lease it.
2)Bandwidth is cheap.
3)There’s no such thing as SEO Fraud if you get a good consultant.
4)You don’t have to deal with customer service.
5)Even non-targeted traffic can be siphoned off somewhere.
6)SEO’s aren’t quite clever enough to implement “smart pricing”.
7)You’re helping to improve search engine relevancy
Natural search arbitrage is usually deemed spam
9)No bid wars, and crappy sites don’t cost you.