Minor league baseball did okay outside for about 30 years before the Diamondbacks came around. Part of the problem is perception - it's not all that bad outside at night in Arizona during the summer. It's still very, very warm. When there are monsoons it can be very uncomfortable. But it's not all that different from what you experience in a place like Texas. In fact, assuming humidity it may actually be more comfortable to play at night in Arizona than in Texas. Doesn't mean people are going to want to sit outside in 100-degree weather to watch minor league soccer though.