This was common practice by car dealers… 40 years ago. The industry eventually learned that satisfied service customers buy vehicles too.
Today’s shortage of Technicians/Mechanics has caused some dealers to start thinking this way again. It’s now common for a dealer service department to be backed up for weeks due to not having enough Technicians. Some dealers have taken to prioritizing customers that purchased the vehicle from them. I suspect that might be what’s happening at the OP’s bike shop.