It's kind of like the theory that open source doesn't have serious bugs because so many people read it.
You know the saying that the market can remain irrational longer than you can remain solvent? If some people don't care about doing simple analysis, and others assume that someone else is doing it, and still others accept that it's useless to do it if other people aren't, it seems like a none-too-efficient market can be a stable equilibrium.