I will almost guarantee you the reason it's set up this way is to prevent people cheesing gear drops. Yes, it feels terrible in party finder when you lose that roll and, whup, nothing for you this week... but the alternative basically would make statics wildly overpowered.

If, for instance, you could go in as many times as you wanted and roll on things until you won something, then you would absolutely have a group where they go "okay, we'll run the first fight, everyone pass on the gear and let <X> win everything." Then they'd run it again, and everyone would pass and let <Y> win everything. And then they'd run it again and everyone would pass and let <Z> win everything, and so on, until everyone had gotten the absolute maximum amount of gear possible from every fight in the tier.

The fact that you get one shot during your first clear, and after that you not only can't roll but also will prevent others from rolling is almost assuredly to try to prevent that sort of cheesing. It doesn't make it less obnoxious, especially when progressing in PF, but I would bet you solid money that if they didn't do this people would absolutely shortcut the gear grind that way immediately.

Allowing for that, the one thing I really do wish they'd change is not deduct a chest when only one person in the group has cleared already that week. Having that one slot of leeway does not allow for open-ended gear cheesing, but it does make it a lot less annoying for a static to find a sub if they're missing someone on a raid night.