I believe it is because fast food restaurants hire ex-cons or do not really care if an employee has been arrested, was in prison, or is now on probation? I know it is like this in pubs and bars, and non-fast food restaurants.
An insane amount. Its far easier to run into a life threatening "OD" situation with cocaine than meth. The problems meth bring are more on the psychological side and depending on other factors, can be unpredictable.