Why do people go to Houston?

For lots of reasons:
1. Jobs
2. Shopping
3. Visit friends
4. Entertainment
5. Compete in sports
6. It's the oil center of the world.
7. Headquarters for large corporations
8. International airport.
9. Attend college or university. Cooking schools.
10. We have foreign embassies here.
11. Medical centers, research of different diseases and genome technology, Cancer Treatment, Childrens hospitals. Specialized doctors.
12. NASA, space center is here. They help fly the International space station. They are working on space tourism.
13. There are lots of oil refineries, chemical plants, breweries, and export/import businesses. I think all the Volkswagans from Germany come through here. There is much international trade in our seaports.
14. Create jobs.
15. Businesses come here because there is no state tax. They can also get tax exemptions on property taxes.
16. It is very diverse, so we attract many foreign businesses.
17. People come here for the arts and culture.

Because Heaven and Hell have onerous travel/entry requirements...;-D...

Airport? People visit a city to see the airport?

Because Dean Martin says it is the place of the warm and friendly.  Why an Italian New Yorker wants to sing about it, is beyond me.

Actually an Italian Ohioan. He was born and raised in Steubenville, OH. But still a fair point.

Not necessarily. They may have to in order to connect with other flights.

No idea.  I've been down to Galveston but didn't even stop in Houston.