Since events are the main way outer world interacts with Duniter, it would make easier to display this value in Cesium for example without having to look into the storage at the block before the event.
The indexers can keep a trace of the value in case of EvaluatedValid to give an order of magnitude, for example "97%" means "no problem" and "81%" means "you might not be able to renew membership without additional certs. In case of EvaluatedInvalid which should not occur if we use an third party service to pre-compute the result before submission, "79%" means "one more cert should make it", and "50%" means "you are too far from the rest of the wot, please meet more people".
That makes sense. I had forgotten that T::MinAccessibleReferees::get() (and the median value) is a Perbill, which should be directly comprehensible for the user.