Perhaps he did not trust the Secret Service and got his own personal security detail?
Reportedly, the SS detail was costing NYC gazillions and the young Trumps were getting bad press about it, and stopped the Service, replacing it with their own service detail. Blocking off streets 24/7 around their residence in the Tower was said to be hurting businesses, as well.
Bet that is why. Traitors all around.
Aside: I really like Don, Jr. He thinks like us, maybe more so than his dad. Not crazy about his sister & brother-in-law being so close to the President.