My layperson guess is that once you're told what to expect to see, you stop looking.

This makes Eliezer's weirdtopia idea of science being kept secret so as not to spoil people's fun of discovery more interesting-- it's not just that people would independently discover the same things (and I wonder what the protocol for sharing information would be), given enough time and intelligence, much more might get discovered.

Someone who seemed a bit better informed

Could be a few things - looks like part of one of the other ligaments, is usually damaged doing a 'standard' dissection, plain old 'you see what you think you should see' bias, some combo of all of the above...

And that comment is answered by:

Medicine needs more Masters and PhD students. I'm sure if they had as many students studying the body in extreme detail, like the eleventy billion English majors who write thesis/dissertations on say, Shakespeare, this would've been hammered out decades ago. XD

Which is interesting-- sometimes studying things in extreme detail "just because" (probably because the object of study has high status-- consider early observations of the planets) can pay off big.