tourism can be so lucrative that it is actually profitable to force out normal people and completely reorient the economy away from all other productive activities. eventually large parts of the city will become totally stagnant, but this doesn't seem to stop tourists from coming. there's often a constituency of people who are really benefiting from tourism (property owners, tour operators, restaurants) and who form a powerful bloc opposed to any restrictions or taxes.
it really seems quite similar to an economy where natural resource profits drive everything, it's impossible to get any other industries off the ground or make enough money to live in any other way.