1. Forgetfulness
2. "Something more interesting came up"

Forgetfulness

Especially when sign-ups occur far in advance, people just forget to show up. An effective reminder usually does the trick. You can rely on your team to send out reminders, but I prefer using a volunteer management tool ( VolunteerSpot is free and really easy!) or an automated service like a newsletter tool ( Feedblitz is great!). Both of these tools can be used to automatically send reminders to volunteers a few days before your event so that they remember to show up.

Something more interesting came up

If "something more important came up" it means that volunteers are not engaged enough with your cause. Even the most notable cause in the world will experience the flake rate if volunteers don't feel that 1: They are a part of something bigger, and 2: They are important to the cause. In a previous post, Volunteer Progression of Needs, I address the different needs of volunteers, as well as provide four tips to improve engagement:

1. Listen
2. Understand
3. Recognize
4. Ask