And new clubs would face an impossible up-front expense. Anyone who performs or plays copyrighted music needs a license. Normally, the event's organizer is responsible for obtaining the required licenses. For commercial concerts, that's the promoter. For square dances, it's the dance organizer.
Most dances are club-organized, so clubs are responsible for being licensed.
When the issue arose, club leaders got worried. So to protect themselves, clubs have started to ask all their callers to be licensed. If you run dances or weekends of your own, you'll need a license for yourself. Those conventions must get their own licenses. You're also covered if you do rounds or Country Western dances as part of your overall square-dance program.