What's stopping them?
What's stopping them is that by not playing by conventional rules, they will not get official kudos in the field. People like Bostrom, etc. who do play by the rules will. One might not care about official kudos per se, but one should -- people with official kudos are the ones with actual sway on policy, etc. Important people read Bostrom's book, no one important reads EY's stuff.
I think this is the vital thing: not 'does academia work perfectly', but 'can you work more effectively THROUGH academia'. Don't know for sure the answer is yes, but it definitely seems like one key way to influence policy. Decision makers in politics and elsewhere aren't going to spend all their time looking at each field in detail, they'll trust whatever systems exist in each field to produce people who seem qualified to give a qualified opinion.
I feel that a lot of what's in LW (written by Eliezer or others) should be in mainstream academia. Not necessarily the most controversial views (the insistence on the MW hypothesis, cryonics, the FAI ...), but a lot of the work on overcoming biases should be there, be criticized there and be improved there.
For example, a few debiasing methods and a more formal explanation of LW's peculiar solution to free will (and more, these are only examples).
I don't really get why LW's content isn't in mainstream academia to be honest.
I get that peer review is not the best (far from it, although it's still the best we have, and post-publication peer-review is also improving, see PubPeer), that some would too readily dismiss LW's content, but not all. Lots would play by the rules and provide genuine criticisms during peer-review (which will lead to the alteration of the content of course), along with criticisms post publication. This is in my opinion something that has to happen.
LW, Eliezer, etc, can't stay on the "crank" level, not playing by the rules, publishing books and no papers. Blogs are indeed faster and reach a bigger amount of people, but I'm not arguing for only publishing in academia. Blogs can (and should) continue.
Tell me what you think, as I seem to have missed something with this topic.