Event invitation lists are vetted heavily by fundraisers and change frequently. If you upload an initial invitation list of 200 and it is whittled down to 50 for the final send, you have to remove invitees one by one (or just start over). If you could multiselect people on the invite list, you could much more easily manage the list before sending.

(Also vote on idea bank item I-796 to allow you to export the list without adding the communication until your list is final)