I've been trying to book LAX->EWR as a reward ticket recently and I notice that there is lots of F available as long as a connection is involved. However I find that most of the connections involving CO on one or both come up with No available BF or F seats for this segment. It's always the CO flight and IF they are BOTH CO flights then I've been getting the warning for the entire trip! This really means that there is NO availability for that routing.

For example: (for travel September 2)

There are no First/BusinessFirst/International Business Class seats available on CO525 in the New York/Newark, NJ (EWR - Liberty) to Cleveland, OH (CLE) market.
! There are no First/BusinessFirst/International Business Class seats available on CO173 in the Cleveland, OH (CLE) to Los Angeles, CA (LAX) market.