There could be several explanations, but all indicate seriously that the field may not be operating for much longer:
1. Low demand: Business does not support paying refs on speculation walk ons will show
2. Owner unavailable: Due to other employment, medical issues, etc., the operator needs to be able to control what dates/times there is activity at the field
3. Other activities: The owner wants to have some weekends free to do other things at the premises. One option would be to do walk-throughs with prospective buyers/developers.