People (in the US at least) bash cops more often than soldiers because cops are the day-to-day face of state authority that we encounter. Certainly, I see soldiers sometimes, but they are not the ones employed to keep me obedient, instead, it is the weight of law, cops, and prisons.
Anarchy is inherently individualistic (as much as it can be inherently anything), and so it makes a lot of sense that cops draw such an overwhelming amount of ire from us. I think the same priority of hating what constrains the individual holds generally true for residents of the US in general. That doesn't mean soldiers get a free pass though.
There are plenty of criticisms of the military and of the myth that troops fight and die for our freedom. Those that are most appealing to me personally combine an analysis of the role of an enemy other (ie "the krauts," "the japs," "the commies," "the viet cong," "the terrorists," "arabs," "islamists," etc...) which serves to create false unity in the face of the inequities of capitalism while also creating a sort of steam valve for discontent and the critique of war as a necessity of maintaining industrial capitalist civilization.
Another piece of why this silence might be is the combination of fatigue and immediate goals. If we take a long view of recent history, anarchists poured a lot of energy in to big picture issues at the end of the 20th and beginning of this century - whether it was the first gulf war, the bombing of the Balkans, the "War on Terror"(tm), or just garden variety economic globalization, anarchists spent about fifteen to twenty years focusing on confronting issues that were beyond our ability to have much impact on. We shut down Seattle? That is nice and all, but it hardly slowed the march of global capitalism. More people than ever before turn out to protest the looming invasion of Iraq? That's cool, they are getting invaded anyway. After a decade-plus of ongoing occupation, piled on top of the decade plus of constant low-level warfare that happened from 1991 - 2001, many anarchists started to focus on the war(s) at home rather than those overseas.
Police violence hits much closer to home than the violence of the military industrial complex (though of course, the cops and military play similar roles in different spheres of operation), so, much as many hate to admit it, we are more likely to pay attention to it. The violence of police has also had some amazingly high profile moments that resonate with folks in the US in the last several years as well (notably in the Bay Area, and Pacific Northwest, but also Denver, the Twin Cities, and reaching back a few years, New York, Cincinnati, many other places - like pretty much everywhere there are cops.
I think that maybe gets to part of it, actually, though I hadn't thought to formulate it as such until right now: the military's presence is felt most acutely where the military is acting, which is overseas, and cops presence is evident wherever law is enforced - pretty much everywhere.
For some other takes on anarchist anti-militarism, here are two links:
http://theanarchistlibrary.org/topics/anti-militarism
http://theanarchistlibrary.org/topics/anti-militarist