Setting the score metadata explicitly (without a results producing stage that also produces a score) in a view definition does not make much sense as a use case.

Furthermore, a $score stage in a view definition only introduces complexity / confusion for hybrid search:

• A $rankFusion against a view with a $score stage, can have the $score's result appear in its scoreDetails, with no correlation to the behavior of the stage (confusing the user).
• For $scoreFusion, we could actually get incorrect results, if the view produces a score (like with $score) and we run a search input pipeline against the view; the way search-on-view is implement executes the view pipeline after the search, meaning the view's score would supplant the search score for that input pipeline.

For these reason's we choose to ban a $score stage inside a view definition