It's not that they perfer non-rated FO's, it is that they like to get some guys in with low time becuase until you have 1500 hours you make a lot less. With that said I was told directly that there were a large number low time 300 hour wonders hired to offset some direct entry captains required and that they don't want their entire FO pilot group staffed with these guys. Expect guys with time on type to be hired for the next few groups.
Whenever that happens.