Sometimes you just want certain posts to just quietly, softly go gently into that good night – whereas an automatic notification on every post deletion is a banner invitation for a lot of infighting.
It’s the same sort of logic that demanded “you must require a comment on every downvote” on Stack Overflow. Reams of discussion you can read about that on meta.stackexchange and meta.stackoverflow. TL;DR – it’s a toxic and dangerous requirement, and ultimately unnecessary, because there is nothing stopping people from adding a comment if they want to.
I think it’s up to the mod to decide if the deletion is a teaching moment, if they have the bandwidth for the teaching moment, versus the headache of sending an engraved “want to get in a fight about this?” invitation every single time something needs to be removed.
I do think it’s a good policy to encourage a PM on deletions, but requiring it (or auto-notification) is quite beyond the pale.