I think their point is that the data shows that previous infection provides good protection. If the goal is protection, then this should count for something, and should be factored in to the risk-benefit ratio. The risk-benefit ratio is not negligible for young, which is why the vaccine still hasn't been approved for the very young (and there's certainly not a step function in the risk-benefit ratio, by age). But, the risk-benefit ratio calculations being used don't seem to be including previous infection. This is not necessarily scientific.
For the other-than-COVID vaccines that are required for enrollment, there isn't existing protection in the majority of the population. Nobody has natural, effective, protection against measles.
I think the practical problem/reason is that there's infrastructure set up to track and share vaccination/booster status. There's no infrastructure set up to track, or even test, immunity status, which is the real metric of risk. So, for practical reasons, proof of vaccination status will always be favored and, almost certainly, held above the true, yet difficult to measure, immunity status, to drive policies. This is an easy out, that might cause harm, relative to an "ideal" policies that were based on immunity.
For the other-than-COVID vaccines that are required for enrollment, there isn't existing protection in the majority of the population. Nobody has natural, effective, protection against measles.
I think the practical problem/reason is that there's infrastructure set up to track and share vaccination/booster status. There's no infrastructure set up to track, or even test, immunity status, which is the real metric of risk. So, for practical reasons, proof of vaccination status will always be favored and, almost certainly, held above the true, yet difficult to measure, immunity status, to drive policies. This is an easy out, that might cause harm, relative to an "ideal" policies that were based on immunity.