What is the story with the 456 trains?

Southern have done what I consider a half-hearted re-furb, they look
very dull inside compared to the 455s, although the new seat covers are
an improvement. The paint work on the outside of them is looking awful.
Southern have touched up the ends of the trains (drab gray) but the
rest of the outsides still look awful.

Is there a reason why these units appear to be so poorly maintained?

They really do stand out as an eyesore in Southern's fleet.