Recently, I have been deleting a large number of posts (the details can be found in my answer on the recent meta post "Please vote based on quality"). Presumably the ones you're asking about were involved in this purge, but I can't explain why any particular post was deleted unless you can point me to an actual deleted answer, as they were deleted for a variety of reasons. Upvotes, especially in the wake of the current situation, are wholly irrelevant.
Due to the very nature of site-moderation, user posts may end up closed and/or deleted with absolutely no notification. Because of how difficult it is for me to leave comments in general, and how often said comments are just taken as something to either be argued with or ignored entirely, I have chosen to forego notifications — especially notifications to established users who should already know by now how the site works — unless I feel them to actually be constructive.
For the most part, I chose not to leave comments because it would only be duplicating information already found in our help centreour help centre. Posts which are, among other reasons, very low quality or which don't fundamentally answer the question asked don't belong on the site.
The fact that a regular user cannot cast an undelete vote on a moderator-deleted post is by design, see also the related meta question "Why deleted answers can not be voted for undelete any more?".