ECS Ball Seat and Conical Stud Conversion Kits

Why use wheel studs instead of wheel bolts?

Because, race car.
Wheel studs are required by many racing bodies because they are a safer way to ensure proper wheel-to-hub contact.
Wheel studs allow the use of different length spacers. Lug bolts require custom lengths per spacer application.
Installing wheels using wheel studs is much easier than using wheel bolts, as the studs will locate the wheel while the nuts secure the wheel.
Wheel studs stay in the hub. The constant installation and removal of wheel bolts can cause accelerated wear on the bolt holes in the hubs.