People are prone to taking mental shortcuts. They may know that they shouldn't give out certain information, but the fear of not being nice, the fear of appearing ignorant, the fear of a perceived authority figure - all these are triggers, which can be used by a social engineer to convince a person to override established security procedures.
I use Mac. Not because it's more secure than everything else - because it is actually less secure than Windows - but I use it because it is still under the radar. People who write malicious code want the greatest return on their investment, so they target Windows systems. I still work with Windows in virtual machines.