Anyone who is volunteering to help with your event supports your mission. And while some are there simply to support, most may have an additional incentive as well. Even though they have willingly given you their time, if you put in the extra effort to help with their other motives for volunteering, you will have happier, more productive, and longer term help.
So, why else would someone volunteer other than to simply support your cause? They may be interested in expanding their network - whether it is to further their business or help secure new employment. Volunteering is a great way to connect up with new people and show them what you can do.
Sometimes the volunteer position itself can help one develop a professional skill. For a volunteer that is not extremely computer literate, using a program such as Pearl Bids can help increase their knowledge and ease around a computer. Pearl Bids is designed to be easy to use, and many of its commands will transfer to other popular programs.
Keep an open mind - and open ear - and see if you can't better understand your volunteers' motives and needs. Perhaps a volunteer has extensive social media experience with several programs, but has never written a blog. An experienced social media user would have no problem setting up a blog on Wordpress, or a similar program, and they would have gained a skill in the process. Support your volunteers and assign them to tasks which excite them and help them to grow and you will find that the productivity and retention rate far exceeds your expectations.