I'm not so sure about that. I'm pretty stingy with my points but I can think of at least 4 trips (out of maybe 10) that have been 3 days or less. We've done a couple 3-night getaways, a short stay when I was in town for a conference and another the night before our
DCL cruise.
We also did a split stay with just one night at the first resort. That wouldn't be allowed with a 5-day minimum.
Minimums have the potential to leave a lot of unused nights at the resorts due to the varying arrival and departure dates. Let's say we have a room that's booked from the 1st to the 5th, and then the next guest is scheduled for the 8th to the 15th. The room would sit empty for the 6th and 7th because nobody could book the minimum 5-night stay.
Overall I think minimums would have a very damaging impact on members' abilities to use their points. Resorts are sold to near 100% and it would be virtually impossible for occupancy to ever reach that level.