1) People need to work to get money to even go on vacations, and having time off allows them to go on vacation.

 
2) The wealthier a country is the more they can pay their citizens for jobs they do and keep technology up-to-date to attract tourists.

 
3) People need a place to stay if they go places.

 
4) If there is at least a way for people to translate into a common language it is easier for transactions to be made in countries around the world.

 
5) People need to know about where they're going to. This way they can also purchase services for tourism without actually being in the counrty they want to be in.

 
6) People need to be able to actually get places outside of their home city/country.

 
7) This gives tourists a way to get to other countries as well as pay within those countries. Without these they wouldn't get very far.

 
8) People need to know something exists to know they want to go to it.

 
9) If things stay fresh in a tourist area it brings tourists back again and again instead of just getting their interest for a one-time trip.