Because governments at all levels think they can tell you what to do with it:

This week, New York state senators vote on a bill that would make it illegal for any homeowner or renter to sublet for less than a month. The new law would be a blanket ban on short-term rentals no matter how ethical the renter is.

Geopolitical note: If this passes, New York State will banning that which is legal in...Communist Cuba.