This is the basic idea. Now onto the concrete situation at hand.
In this setup, there is a real threat of bombs for scum. If all they know is that someone has a PR, but not which one, then they will hesitate to kill there. This could have been a factor that protected town!scola tonight (and similarly town!fang). But from an analysis perspective, a reduced PR/no-PR claim is unsatisfying for town: On one hand, you cannot catch a fakeclaimee in a lie this way, and on the other, if we exile someone without ever knowing what PR they are, we may well lose important information on what night actions they performed.
Thus we are in a bind: from a scumhunting perspective, fullclaims are desirable, but for creating the optimal position for town at night, we don't want them.
A no exile today allows us to keep claimed (and unclaimed) PRs in a useful limbo state for the night, and at the same time, we are not sacrificing too much because we don't need the fullclaims today (which would be the case, I would argue, if we wanted to maximise the odds of exiling scum today).