As much as we like what Fitz has done for us we have to remember his history. As great as he can look at times, he is very erratic. I'm not sure I've seen a QB lose a starting job more than him.
If Fitz struggles at some point early on, the team could obviously go straight to Tua. But there is also a chance that Rosen can fit in a few games to showcase himself, before that happens. And while I do believe Tua will play this year, that decision is not set in stone yet.
And don't underestimate how easily Covid could lead to him getting an opportunity. We will see a lot more backups playing this year than ever before.
Rosen is going to have a tough time finding starting snaps anywhere at this point. It would make perfect sense for him to see how this plays out before asking for a trade.
Everyone knows he's not the future of this team. But the real benefit of him getting snaps with us would be to increase his percieved value. Which in turn, gives him a greater opportunity to start on his next team.
If he wants to really get a shot at being a long term starter, easily his best opportunity would be to wait for another team with a weak backup to lose their starter to injury. If that teams comes calling for Rosen, we get to cash in on their desperation and he gets his chance at a job. Everyone wins.
(But all of this assumes the plan isn't simply to have Rosen be Tua's backup after this year)