I've got several reasons:
1. Pretty easy to get to with 635 and the DNT.
2. Pretty safe, Addison police are asses so they're always scoping suspicious people. So for providers they don't have to worry about getting mugged when leaving their room. However they just have to be discrete enough not to get busted.
3. Couple of hotels there know this (above) so work out deals and keep watchout with providers to keep their rooms booked.
4. Good mix of blue and white collar businesses for a steady stream of customers.
5. It's close enough for us suburbanites to see providers, but far enough from our homes to not get pinched while our SO's shop at Stonebriar and Willowbend