The environmental factors are definitely the primary causes. People won't do anything to change this. The amount of selfishness and apathy within the human race is pretty disgusting. Even if you explained the current situation of the bees to most people they wouldn't bat an eye lid, let alone attempt to do anything about it.
a couple things. to say that environmental factors (EF for short) are the cause of extinction isn't really to say anything, though. I absolutely don't mean to sound condescending, but the most basic underpinning of Darwinian evolution is the idea that a species (or population) gradually adapts over time to its environment by the natural selection of traits which are favorable to survival in that environment. so EF are always the "primary cause" of extinction, as they are the primary cause of all evolutionary success or failure. what you really mean by EF, I think, is changes to the environment caused by humans, yeah? the thing is, "environmental factors" is a staggeringly huge & diverse category. not only is it often very difficult to pin down cause & effect generally, but it's also usually very difficult to draw any kind of definitive line where human cause stops & factors beyond human control take over. that's simply the nature of science, especially when dealing with something as endlessly complex as an ecosystem, let alone the world as a whole. that's not to say that there hasn't been a massive human-driven effect on the environment; almost (like 99.99%) certainly there has been. but it's one thing to say that, & it's another to produce hard data about
specific issues that can convince policymakers to institute change, or their constituents to demand it from them (admittedly this is also very much an issue of media, how science is presented to the lay public, etc). there's also the problem of developing a correct strategy, which again, usually isn't easy. what "should be done" about bees? keep in mind that any strategy implemented has be to be feasible or it's not worth implementing in the first place (i.e. one can't just demand that people completely stop using fossil fuels tomorrow - or you could, but obviously it wouldn't happen).
sure, humans can be selfish & apathetic. going on about it doesn't help anyone. individual selfishness & apathy isn't really the issue - certainly, it doesn't help, but realistically we're talking about massive readjustments, not only structural (tho certainly those) but also in the way we approach life, organize our societies, etc I'm not arguing against personal responsibility, in fact the opposite. but say an individual does devote his or her life to bees - there are still a hundred other issues of equally pressing importance. further, the great majority of people simply are not in a position to devote their lives to bees or anything else even if they wished to. we most of us have to spend the bulk of our time dealing with day-to-day economic realities, which is not unconnected to the environmental stuff, as well as another place where the readjustment business comes in. the real issue is whether it will be voluntary or involuntary, as things get so mucked up that what we have now simply isn't sustainable. I obviously hope for the former but I rather fatalistically tend towards the latter. either way tho, complaining about selfishness isn't really doing anything.