1. Because the AR is so versatile and flexible, more so than any other rifle at the same price.
2. Because I like the design, internal and external.
3. Because you can make so many modifications yourself using common tools.
4. Because the aftermarket upgrade selection is mindboggling. Calibers, barrels, rails, optics, you name it - someone sells it and will deliver it to your door.
5. Because I carried an M16 in the service.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek