There are good arguments for teams as to why they keep 2, and others 3. And I'm sure the reasons they make those choices vary.
For those that keep 3, it could be that they have a 3rd QB they don't want to risk losing.
It could be that they have a concern that if QB1 gets hurt for any extended period of time that suddenly they'll have to acquire a back up for what was QB2 if they don't have a QB 3 on their roster (and any decent QBs are already on other teams).
It could be that their QB3 is the better of the available players on their roster (at any position) as they get near the bottom of the roster. So it's just a matter of keeping the best of the talent they have, overall.
There's probably other reasons I haven't thought of but the point is that yes, many teams keep 3 QBs among the 53. But McVay typically has not. Will that change because Perkins has shown so well? I think it could, especially if he lights it up again in the 3rd preseason game. Like pitching in Baseball, there is no comparable position of value on a football team than the QB.
We'll know what McVay and Snead think in a couple more days.
