Arizona was a place to get through as quickly as possible. Places like Tucson and Flagstaff were stops along the way to and from California. While Spain was building a Mission near Tucson in 1797, the area that would one day be called Phoenix was a very wild place, with two warring groups of people, the Pimas and the Apaches.
But Phoenix, Arizona ultimately won out and has become the most prosperous and most modern city in Arizona. There are many reasons, most of which are small, but they add up.
• Gold. No, the gold wasn't really in the Phoenix area (although some of it was). Mostly it was at Wickenburg. And Wickenburg did prosper for a while, as did Prescott. But Phoenix had an advantage that these other towns didn't.
• Agriculture. The Salt River Valley is one of the most fertile places on planet Earth. All it needed was water. And luckily, the Salt River Valley is at the bottom of one of the largest watersheds on planet Earth. People can't eat gold, you know.
• Phoenix is north of the rivers. You may say "what rivers?" as they have been so completely tamed now as to be virtually erased. The two rivers are The Salt and The Gila. Sure, you can cross them so easily now that most people don't even realize that they are crossing over a river, but in the 1800s they were virtually impassable much of the time. So, if your town was south of the river, you were at an immediate disadvantage in relation to what was really happening at the time - gold mining.
• Financing. Phoenix immediately became a town of banks. All of that gold had to be stored somewhere. Valley National Bank stored quite a lot of it, and then lent it back out, which built Phoenix businesses and homes for almost 100 years. It continues to this day with Chase Bank.
Arizona has many scattered ghost towns, and cities which stopped at a certain time. They are great tourist attractions. But if you visit Phoenix today, you will see that it is still growing. It was built on its early success and continues to prosper.