Because he wanted a place were families could all have fun together. He felt that this was not being done in other locations. In creating Disneyland in 1955, he established a model that became the standard for the theme park industry.
Disneyland in Anaheim, Disneyland Paris, Tokyo Disneyland, Honk Kong Disneyland, and in 2014 Shanghai Disneyland Walt Disney World has a similar park to Disneyland called the Magic Kingdom but it is not named as such.
There is one Walt Disney World resort, in Florida. There are four Disneyland resorts though, Disneyland Paris, Hong Kong Disneyland, Tokyo Disneyland, Disneyland (Anaheim), Euro Disney, and there is soon to be a Disneyland in Shanghai.