Some pilots may live by the airport, have no kids, no spouse, don’t mind leaving their ringer on all the time, and love going to work. They don’t even need 24 minutes - they can accept and acknowledge in 1 minute.

Other pilots may be interested in flying green slips, but have a lot of other commitments in their lives that need to be rearranged before a slip can be accepted. They may need 2-3 hours to hear back from everyone to determine whether they can commit to a trip.

Most pilots are somewhere in between those two extremes. Unlimited batch sizes decrease the pool of pilots for whom green slips are practical, driving them more junior overall.