Of course, the Rams could not make any substantive QB moves because they believe that Keenum is going to improve a bit - and the Rams were winning with him. They may believe that the project QB they took in the 2015 draft will be ready to become a starter at some point this season, and that the QBs they can get without a massive, risky trade, won't be ready to start as soon as Mannion. They might not do what you want, based on information they have that you don't.
Or they could just be wrong, of course. Wouldn't be the first time. But never believe that Fisher and Snead aren't trying to win. They are, even if it's not the way you would do it.