I don't know about SF's attitude in Mexico, but advertising isn't just to compete with others. Advertising is also used to create demand for a product. Even if you are the only park in town advertising can help to get people to come to the park instead of staying home or doing something else.
When I was a kid. Pontchartrain Beach in New Orleans was the only real amusement park for hundreds of miles. They still advertised heavily in season to encourage people to come out and spend their money.