(d) a lot of people buy into the "school is worthless" line so hard that even when something as practical as state machines are paraded in front of them they don't notice
(Granted, the education system might have some responsibility there, but personally I recall examples being made. There's only so hard the profs can make the point that this stuff actually matters.)
(a) just because you covered it in a class doesn't mean you remember it five years later
(b) lots of people rise through the ranks of IT without formal CS training
(c) some CS programs are not so reputable