Usually, other commitments in life - work and family, not that there's anything wrong with that - are what keep me from an event. This weekend it may be torn ligaments in my knee. But how much flexibility do I really need in my right knee anyway? Todd already volunteered everyone else to do my heavy lifting.
Entry fees being a bit high would be my only complaint that NASA has any control over.
Gas prices and my POS tow vehicle etc. are out of their control.