Accessible seems to have crept in, perhap from wine tasting, where perhaps a literal translation of a word which perhaps has multiple meanings in one language yet the same word doesn't share all of the meanings in another.
Think of the example - "The black run is easily accessible by a chair lift number 3 as is the blue."
Accessible means it's easy to get to and not a term that most native English speakers would describle how easy it is to ski.
If you want to describe the difficulty of a piste then stick with simple terms like easy, moderate or hard or describe the skier that would be expected to have the ability to ski it enjoyably so beginner, intemediate or advanced.
