Hey there,
that is a fair question! I wasn’t fully aware of the unpublish_date especially. The thing is, these events can potentially have an end date… also I have set up an extra tab with only the relevant fields to fill out, to make it easier for my clients who are very usually not tech savvy at all. I guess I could repurpose the publish_date field for the start date, but it might result in some confusion. And setting the unpublish_date just adds an extra field to fill out with the same data as the start date.
– But I might repurpose the unpublish_date field as the start date, now that would be something! That would save a bit of date checking in the templates. I will think about that for a bit; it sounds like a good idea for my use cases, but other people might have different requirements. Still, thank you for telling me about it! 
(And if you happen to know how to actually delete pages, that question is still unanswered…)