1. Remember the NBA has legal zone defense.
2. Additionally, help defense is a lot easier in today's NBA. Forced isolations would be very difficult and even if you do it, there is less ground b/w help defense and the attacker.
3. You have many more quick and/or lengthy 3&D type wings in the NBA today. Help and close-outs are easier.
4. Long shots mean long rebounds. Putting wings one step in means the offensive team would lose out on one of the main disadvantages of zones - inability to secure defensive rebounds.
5. That one player will also be a liability on transition D. He will always be one step behind in case the opposing team forces a TO and runs.
That's just scratching the surface, but there is a reason it's called no-man's land for shooters.