Even if the backups are better now than the starters that might not have been the case a few weeks ago. My take is that it takes a lot more to play pro ball than ability. If these newbies have better skills that's great, but even so they can't get on the field until they know how to play within the scheme.
Why did it take so long? Can't say for sure, but it takes time to get up to speed, and obviously some longer than others. (Just to throw a name out there, Littleton didn't start until his 3rd season.)
But then why did we see these guys earlier in the year? One possibility is the coaches saw their ability and found a few situations where they could send these guys out there with a limited game plan (even though they weren't ready to start).
AlbaNY_Ram