People in different communities need help and volunteer support but on the other hand, people are very busy and do not have time to participate, so how to reconcile between buy people and volunteer work.
Volunteer work attracts people who—in no particular order: (a) want to contribute to a cause in which they believe; (b) need to fulfill social expectations; (c) are motivated by a desire for change; (d) want to have a sense of ownership and control (that they cannot find in work situations); (e) want to learn new skills; (f) want to enjoy what they are doing; and (g) want to meet new people. Volunteer engagement programs that cater to the above-mentioned needs will help attract volunteers; such programs will also help retain volunteers if they recognize that the three primary reasons why volunteers leave an organization are that—in descending order of importance: (a) they were underutilized; (b) the physical environment did not support their efforts; and (c) the atmosphere was impersonal.
A really interesting question and a great answer from Olivier too.
I wondered if there was also a further category of attractant for a minority of people...do they volunteer for egotistical reasons?
The only reason I mention this, is that I have some experience of voluntary work in the education sector and did come across one or two people who offered very little in terms of knowledge or skills, but seemed happy to simply be part of decision making processes or to have access to information the wider population wouldn't. This is subtly different form meeting social expectations or proving 'worthiness', as there weren't expectations to meet - the individuals simply wanted to promote themselves or get involved as an exercise in self-aggrandisement. Small voluntary bodies with a governance remit, such as charitable or school governing bodies/boards (where good volunteers are sometimes hard to come by) are typical places where you might find this.
I also came across people who joined boards on a voluntary basis, to gain and use 'non-executive' experience on their CV. In turn, they could then secure financially lucrative executive positions (that required 'board level experience). Arguably, talented people would add value and contribute to the organisation whilst they are volunteering and this is a smart way of them breaking ceilings / executive recruitment criteria? None the less, I wondered if a motivation to further career self-interest, goes beyond Olivier's option d)?
Lastly, I have heard about folks who volunteering as a "moral offsetting" exercise - for example, they would volunteer to work for a charity of healthcare organisation, if they worked in a profitable - but contentious - area of corporate life. "Moral guilt" (individual or organisational) might also be a motivator for some to volunteer?
Anyway, hope these random thoughts might be helpful to you - great question and good luck with your work on it!