My point was that if the open office plan is scaring anyone away, it hasn't yet (in my experience) impacted junior developers who are still quite enthusiastic about Facebook. Facebook doesn't only hire experienced developers, and even their experienced hires may not have a formed opinion on open office environments.
There are plenty of people who are biased about things (like an open office environment) they haven't personally experienced, yet hold their bias based on hearing about the experiences of others.
I've never been in an airplane crash, and I'm pretty sure I never want to be in an airplane crash. I don't need to personally have that experience to have a bias against it.
If you didn't know about storage heaters or single glazing before renting a flat, there are probably a number of ways you could have discovered those things without having to experience them directly. It certainly wouldn't require "magic" as you say.
If a bias against open offices is happening, it doesn't seem to be impacting our newest industry entrants yet.