It could be due to the liability laws in your specific state.

I've had my car in for service 3 times. The first two times I got a loaner, the third time I asked if I could wait. Honestly I'd rather wait the hour then get a loaner.

Two reasons I chose my dealership: 1) it's top rated, 2) it's a few miles from work making it extremely convenient to drop the car off for service.

 

Miller Infiniti: I'm asked if I can wait for the oil change (under an hour), but if not, and there is a loaner available, it's been offered. Sometimes they're so strapped for loaners I get shuttled to the Enterprise down the street (on their dime for service, not oil change).

Parkway: Was told they don't offer Infiniti loaners and that I could walk to the rental place down the street (I called in, told them they could go F themselves).

Metro: Always a loaner available as long as I let them know it's needed before I arrive. Oil change or otherwise. Metro is a bit of a drive for me, but I often go out of my way to take my cars there because their service is first rate.