1) Because jobs such as this exist,
2) Because the people hiring for this job have no qualms about describing it in this manner [bold in original]
THIS IS NOT AN ENTRY-LEVEL POSITION. Please apply only if you have at least 5 years of Executive Assistance experience supporting a senior partner, Member of Congress or other top-level executive, and you consider yourself to be a "career EA."
We are looking for a “traditional” executive assistant to report to our Founder/President–the type of assistant who understands how to support one executive and has a “mission mentality” to make sure he always looks good.