People may choose not to participate in or support community policing for numerous reasons. It could be due to the simple fact that they just do not have the time. For example, many people may work twelve hour shifts or even work two jobs and extra time is scarce. Another reason may be due to personality. Some people become very active in the community while others may not feel comfortable doing so. Keep in mind that just because someone is not taking an active stance in the community does not mean that they do not support the community. There are "silent" ways to support the community such as making monetary donations.
This has actually been a big topic of discussion with my home owner's association recently. As we look at our budget and the possibility of raising community dues again, the question comes up, "Where does all the money go?" One of our biggest problems for a while was the amount of litter accumulating in our parking lots and around the dumpster. We discussed the necessity of hiring someone to come in and pick up or policing our neighbors.
Most people said they'd rather pay more money and hire someone than hold a neighbor accountable for his or her actions. I think, when it comes right down to it, humans in general do not like confrontation. People are usually very good at complaining, but when it comes to taking action as a means of stopping negative actions, most people do not think it is worth the time nor effort.
I think other people are actually afraid of confrontation. They truly believe it will result in something personally worse (whether a physical fight right then, or simply being badmouthed and disrespected later) for themselves which isn't worth the chance of bettering the community. I would say this is actually a really big problem in many public high schools and middle schools. Many teachers do not like the idea of confronting negative student behavior because of the potential conflict that might arise. As a result, the few teachers fighting the hardest never feel community support, and generally speaking, the community suffers.