A team may think Bozak is the better player - but Bozak is signed for an expensive multi year contract, which makes him unappealing. A team may be more motivated to trade for a lesser player in a cheaper and and short term co retract.
Just because here isn't a market for Bozak (or Lupul for that matter) doesn't mean there won't be one for a Boyes, or Glencross, ect. Contracts matter - especially for a playoff bound team that's tight against the cap but still wants to add depth. It's a lot easier to add a player who comes worth a 1 million dollar cap hit than it is to for 4,2 million.
The problem lies in disposing of a future better asset to obtain a lesser asset just because you want to trade now.
Boyes has not had any interest in over a few years so there is no evidence to suggest all of a sudden there will be. Glencross got a 2nd/3rd if he shows he can play at the same rate then room can be made without sacrificing a potential good asset.
Bozak has a caphit of $4.25M which is not huge or unmoveable. If someone needs a serviceable center Bozak is young and could get a return. Maybe not now, but come TD if bozak plays well someone could grab him - may actually pay more if bozak is performing and not just a rental player.
Bozak has value and can be moved at some point and it is crazy to just discard him because Boyes, Seto or Glencross may have potential to grab a pick.
Not currently being movable does not equal not worth anything especially for a team in no big hurry.
This is a full rebuild so I'm not sure where this urgency is that we have to get as many draft picks now as possible or bust. A 4th this year is still not as good as a 2nd next year.
I'm more than happy to keep a player and wait than to discard them for immediate returns.