The reason I have encountered most is that people have other interests (obviously situated within the capitalist context) and that these may tend toward an escapist and/or distracted mind set. Packaged leisure activities, media spectacles, and especially sporting events consume much of the remaining physical and intellectual energy for many working people that are not otherwise struggling at subsistence. Anti-capitalism may never be (or seem to be) exciting or interesting enough for some people wanting an escape or craving excitement of some sort.
I can add but little to the reasons listed thus far by you and ALC. Those are great examples as well. People are indeed misinformed about capitalism. Confusion runs deep throughout society, as do various erroneous assumptions about what capitalism is, what it is not, and what it is capable of. And this, coupled with the a fore mentioned media-induced delirium, makes the challenge all the more great for anarchist and anti capitalist.
I do, however, think that one of the most interesting things anarchist intellectuals can do is to point out to working people the irreconcilable divide between work place safety rules vs capitalist demands on production. A working persons imagination can sometimes be captured thus as it exposes a stark reality of capitalist exploitation, while simultaneously validating the individual experiences of the wage-slaves themselves. This is usually best to do after a co-worker complains about something (even if it is as benign as boredom). This is powerful in that it points towards opportunities for agitation and possibly informal self organized struggles within the workplace. Referencing news events in which anarchist are involved provides a broader context for wage-slaves immersed in their own everyday lives as well as topics for further discussion.
Also what ALC said about temporary autonomous zones is indeed valuable. I see it as a combined effort of street based struggles, work place struggles, and anarchist cultural agitation/education.