Or more likely, they are maintaining a number of classes of loco. I would find it hard to think it's only 60s maintained at that depot. And 66s are surely rather reliable. They are after all, good old GM/EMD tech.
But they did sell some 60s. So are they really holding the rest on competition grounds, or is it nobody is interested in them due to either the current downturn or other reasons? If the former, then sadly they are their assets to do with as they see fit i'm afraid. If the later, then that's just how it is, nothing anyone can do about it.
DBs have put them up for sale quite a few times. The earlier attempts failed to get any buyers due to one reason or another. I'd guess that they offered the shabby ones on a policy of "what you see is what you get".
However once the super 60 project got underway I think there was renewed interest. DBs offered up for sale a few that were harboured at Crewe Diesel works under a roof. So these were obviously the best examples that were not currently in service.
Once Colas showed an interest a deal was struck with DBs I believe even offering a service agreement on them. The problem was as soon as Colas got totally refurbished class 60's x10 they did something what could be considered by some a bit below the belt. Which was to fight for DBs contracted work, on which I believe they won on at least 2 accounts.
So now we have a situation (I can't confirm this) where Colas are running paths that previously DBs ran, with ex DBs locos which are maintained by DBs. Even the drivers at Colas were trained by DBs.
So overall, it was definitely a business decision at DBs that involved a lot of shooting of the foot.
No wonder they are shy now.