It’s reduced so that people going from one race to the next have extra time between races (to invite friends, re-matchmake if you end up in a dead lobby, set all 3 qualifying laps etc.). Previously if you daisy-chained events you would have less than a minute before entries closed, which isn’t ideal if you need a little more time to get ready: Featured Multiplayer - Entries for Short races close 2 minutes too early (1912216)
Essentially Short is like Medium/Long now in that if you’re doing races in succession, you’re doing every second race on the list, instead of all of them.