I think this equates to the old "I found it in the last place I looked" phrase.

How many times do you check and the outbound is unavailable? Many. Chances are, you never check further.

So.....you don't really KNOW if that return is available because you don't go past step 1.

Consequently, you are more likely to not get a return because you've simply narrowed the field on the outbound as it is. (Am I making any sense??? )

Often, I *DO* check the return to see if I am getting scammed. Say I am trying to go JFK-HNL-JFK, and the return is unavailable. I will then check it as a HNL-JFK-HNL flight. Invariably, the 'outbound' from HNL is unavailable as well.