Why are some ferrets fuzzier than others?

Some ferrets have bald tails because they get "rat tail" which is simply the tail needs to be cleaned more often as the pores are clogging up and are forming into blackheads which makes it so the hair can not grow. Cleaning the tail and getting rid of the blackheads will help the fur grow back, keeping the tail clear of blackheads the fur should return back to the fluffy normal style.

Some ferrets have bald tails because of a health issue called "Adrenal Disease" this is where the Adrenal gland is not producing the right amount of hormones and is causing the ferret to go bald. This, if left untreated, can end the ferrets life sooner than liked. Ferret tail in the picture is of a ferret with Adrenal Disease. Many ferrets in the USA get this, as they are typically mass bred by Marshall Farms. There are treatments for this health issue, that can easily return the coat to the fluffy coat of a standard ferret.

Some ferrets are fluffy, but not to fluffy, these ferrets are normal ferrets that are probably healthy. Coat quality shows the health of a ferret pretty good.

Some ferrets are SUPER fluffy with really long fur, these ferrets are called Angora ferrets. Like Angora rabbits they are bred to have longer fur than a standard ferret.

Some times it just goes back into genetics, during the summer ferrets fluff wont be as thick. The hotter it is, the thinner the coat. The colder it is, the thicker the coat.