Experienced players may also buy a skip on an alt character. You can be everything on a single character, but some people still want another for any number of reasons. And ive also heard of people paying for a skip for a job that starts at a higher level so they can use it for the story from the start. Overworld content may be trivialized by being 50+ levels above, but all the most important stuff happens in level-synced instances. You being a level 80ish samurai doesnt matter if the dungeon you need to clear locks you to level 18.