3 reasons,
1. it used to cost alot more, prices have really gone down in the last 10 years or so. So people still have that conception.
2. It really is a relative term. $500 may not seem like alot for you or me but for some people it is a fortune.
3. alot of similarly priced hobbies have long term use of equipment, airplanes can easily crash so the cost gets higher.