Bounty Builders have one of the softest fields at Pokerstars. Usually it is the tournaments which are getting advertised, where the less experienced players go. A good example: Sunday Storm and Sunday Million both are very soft compared to other $11 and $215 tournies. If a fun player have $215 to play for on a Sunday he would never pick a regular small field $215 tournament (or regular tournament compared to a Bounty Builder). He will always pick the Million.
It is just like products in the real world. If the consumer doesnt have any experience with a certain product category, he is going to pick the product which is best advertised - the product that is top-of-mind.
Also it is often in these tournaments (Bounty Builder, Sunday Majors and so on) where the prizepool are much bigger, and where the dreams are bigger.