Most of the Bacteria and Molds That Grow on and in Humans

Most of the bacteria and molds that grow on and in humans don't grow well in a lab. Why is this?

A) They are not very resilient, so when they are moved, they usually die in the process.
B) Labs tend to be very sterile so few organisms can survive even if scientists are trying to grow them.
C) It is generally difficult to grow specific bacteria in a lab setting.
D) These organisms tend to be very specifically adapted to their habitat on a person and that habitat is difficult to duplicate in a lab.
E) These organisms lack the usual RNA that would identify them, so it's impossible to isolate them from each other.