You're right. Mack never entered into negotiations. The only difference I see between what we're saying is extremely minor. From what I've read, he did want and request an extension. However, the Raiders told him they were gonna wait till the next year b/c they needed to take care of Carr first and he understood that.
As for Donald, I think the Rams would like to do right by him and not keep him on the cheap with year to year deals with tags, but it's still a tool in their pocket.
So I agree with you to a certain extent: that there are risks to the Rams looking bad, that they don't want to look bad, and would strongly prefer to treat him fairly by taking care of him with a long term contract.
But there are limitations to those desires.