This does not mean that they are bad people that don’t care about their environment while we who actually do volunteer are practically holy -No.
It just means that volunteering does not fit in their life, that they maybe do not have the necessary resources which can also be “just” time and that for some reason they do not take the initiative.
To explain why some people show altruistic behavior while others don’t, psychology has a number of theories. One of them is the five step decision model by Darley and Latané. It was initially designed to explain the existing or not existing assistance in case of an emergency like for example a car accident but I will try to transfer it to volunteering.
The first step that they propose is awareness. The subject has to be aware of the emergency or in our case of a problem in the world that could be solved or at least bettered by volunteering. However, this awareness can be prevented if the subject is lacking time or occupied with its own problems.
If the person noticed the matter they have to actually perceive the matter as a problem and not just as a random circumstance that does not need fixing. This should be relatively easy but there is a psychological phenomenon, namely pluralistic ignorance, which can make it harder. If many people ignore something you are most likely going to assume that this is normal and the right way to deal with it. So if you have many people in your environment who don’t think a topic is relevant you might think so as well. This is where media and organizations like Praxis play a big role. Tough it cannot always change already formed opinions, it is still important to try and reach people who might not be searching actively for this topic to give them a consciousness for what actually is a problem.
If you noticed a problem and also categorized it as a problem, you still have to take responsibility to solve it. Again there is a psychological phenomenon that can hinder this: diffusion of responsibility. The more people are involved in a matter, the more each person hopes consciously or unconsciously that another person is going to work it out. Th problem is that often this hope is false. We cannot always wait for others to fix societal problems but take initiative.
The 4th step is about competence. If you have the necessary competence to volunteer maybe even studied something helpful you are more likely to help. If we make it easier to require new skills you need for volunteering, maybe more people will feel confident enough in their abilities to make a change.
Finally, if we can cross of all the steps before and say: Yes, there is a problem, I am responsible and competent. Then we still do a cost-benefit calculation. Which negative consequences would it have for you not to help? Contrary to car accidents were you are bound to help, in case of worldwide problems like violence against women there are mostly no legal restrictions for not helping. A negative effect could be also a bad conscience.
As a benefit you could for example count the gratitude of the people you help.
Some people may be shocked now: What? People don’t only help for the sake of helping? We have to say goodbye to this idealistic and frankly unworldly view, accept that there are things that influence our willingness to help and use this knowledge actively.