Why do universities announce interviewees for positions as lates as possible? My (R1) university is hiring a number of upper administration positions. We keep getting these emails about the dates of the interview, but the names aren't released until 24 h beforehand.

My previous (large) department did something similar for our chair search, although I think the names were released more than 24 h earlier. 

Why is so much secrecy necessary?
The people who are interviewing for these positions have existing, usually high level, positions at other universities, and care greatly about not having their current employer know that they are looking for other opportunities, to the extent that this can be helped. So the interviewing institutions do the best they can to keep the shortlist candidates’ identity hidden for as long as practically possible.

Thus, balancing out this need for secrecy with other practical considerations leads to the practice you are describing.