I suspect one reason (among many) that AW has trouble getting traction as a partisan issue (or mainstream issue - partisan or not) is an often tacit, sometimes-almost-subconscious concern people have about a slippery slope into utilitarian radicalism. If we start worrying about AW for mammals, why not birds, fish, insects, wildlife ...?

But with, say, civil rights, there is a clear stopping point - all people (within the country) get the same civil rights and that's it. No slippery slope. 

From a rhetorical standpoint, getting more people interested in AW may require finding ways to frame the issue in a way that quells this concern about the slippery slope. Whatever one thinks about full-on hedonistic anti-speciesm (the basis of Singer's Animal Liberation if I recall), it doesn't sell. 

Though touting high-brow philosophy is never good politics, I think many people are looking for a kind of framework to allow them to care about AW without going "all the way" - something that fear of the slippery slope currently prevents them from doing.

There are a bunch of non-utilitarian philosophers/ethicists that have put forward frameworks for caring about animals that don't seem lead to a slippery slope or at least are much too vague to pin down what they do and don't lead to (even better!). If and when there is a need to have a philosophical foundation (or at least purport to have one), perhaps these frameworks should be gestured at rather than hedonistic utilitarianism.