They like their guys....
Gallimore
They tried to trade Hill, he was released, as they tried to trade Gallimore as well, no takers. So Hill was released, Gallimore kept for depth.
How about Bohanna instead of Gallimore? Which one has more trade value, and which one helps the team more? Either way, a team would need to be in need of a DT really bad to trade maybe a conditional late pick.
Joseph
Same as above, it would take some injuries to get a late round pick. As Dallas likes their ST's players saw ell.
Armstrong
Now he probably has some trade value, but Dallas views his value in the rotation more than trading him. A team would have to offer up something pretty good such as that 3rd, or a 4th conditional to a 3rd. Then do you really think Dallas would do it...as we say...they like their guys....
Mckeon
Don't think you can really get anything for him. Many TE's like him are out there. If very lucky a late 6th or 7th, or a player swap. We may want OL depth, another team may want TE depth.
Bell
I think they still like his potential and with contracts expiring after this season, they rather play the long game and keep him.
But as with any player if a team offers there right picks and / or players, you have to consider it.