What Makes Motivated Sellers Want to Sell to Investors?

[Account Closed]

I've learned a bunch over the course of the past few months, both by reading whatever I can get my hands on, as well as some of the great posts on this site.  For someone like me who is just starting out in real estate investing, the overwhelming majority of material I've read suggests that finding motivated sellers so you can get a great price on a property. 

I understand that things happen in life.  People need money, or they miss some mortgage payments, and maybe they're going to be foreclosed on.  My big question is... even if someone is about to be foreclosed on... why wouldn't they just sell their home and get fair market value for it?  This is the part that just doesn't make sense to me.  Even if they're under water on their mortgage... why would you take an extremely low offer from an investor, over just putting it on the market and getting way more? 

Is there something I'm missing?