Believe it or not, that's not actually true. Pokerstars looks for people who have an influence on the poker community. You could essentially have no accomplishments, no big wins or SNE.
For example, you could have someone who is a winning playing at 1000nl and has zero impact on anyone in the poker world, have no blog, no twitter and basically just play poker who wouldn't get a contract on stars for this reason as none is really interested in these players.
On the other hand, you could have someone who is a breakeven player at 200nl possibly even losing player but wins money from rake back but has a huge amount of following and influence so can promote pokerstars much better than a decent winning player. Stars and most other companies I guess look at what they get out of it, if they feel someone is going to attract a ton of new players or going to promote the site well they would rather rake them on.