GitHub lets you do this, but only when writing a review for someone else. Not when addressing someone else's review, in which case your complaint 100% stands.
And yes, it absolutely drives me nuts, honestly. Why can I batch review comments, but not resolutions! Another thing Gerrit gets right! GitHub... Please...
... Another thing that mailing list-based development gets right ;) Most MUAs should know about a concept called "Drafts". I can have as many draft messages concurrently as I want, I can work on them over several days, and I can send them out (in practice) as a batch.
And yes, it absolutely drives me nuts, honestly. Why can I batch review comments, but not resolutions! Another thing Gerrit gets right! GitHub... Please...