The people I interviewed (admittedly only three, but the ones who I thought had the strongest resumes out of their cohorts), were unable to complete even basic real-world programming tasks during the interviews. I would literally sit them down, show them my code base, and ask them to make a minor improvement to a page (i.e something that would take me <10-20 minutes to do myself). None of them got close to finishing the task in a reasonable way.
I think the basic problem is that programming is hard and learning to do it at a professional level takes a lot longer than 8-12 weeks. Much like learning to be a lawyer takes more than 12 weeks -- you wouldn't hire a criminal defense lawyer who had graduated from a "lawyer bootcamp."
If you actually do have the skills to do the job, the best way to demonstrate it is to build a complete, functional, polished website and put your code on Github. Some candidates I looked at had "bootcamp demo projects" on Github but the quality of them was way, way below where it needed to be to prove they were adequately skilled.
As they say: "show, don't tell".