The calendar is full of events hosted by other organizations. Their fundraisers are painted across the coming months in broad strokes. The charitable golf tournaments are ubiquitous. Speakers are scheduled every week. The running schedule has the biggest race of the year on the weekend you selected for your neighborhood 5K.
If you require everyone to participate in your activity then this is a problem. If you need those who believe what you believe then coordinate the event’s schedule with only a few other like-minded enterprises. There is always an excuse to postpone but so often it is driven by fear and rationalized by pointing at what could go wrong.
If you have found shared purpose then the event is not just yours but it is ours and I am putting it on the calendar.