They offered this OP uber credits (its in their post).
Basically, they took the car in for non mandatory service (nothing broken, but a "checkup"), and did not attempt to verify before said appointment date / time that there would be loaner cars available, then was surprised and disappointed when there were no loaner cars available.
No brand "guarantees" loaner vehicles. They are normally provided depending on availability. If one requires a loaner car, then, especially if taking the car in for service that is not impacting the ability to use the vehicle, one should contact the service center and find out what is the process for ensuring they can get a loaner.
That might be scheduling your appointment at a specific date / time, like first thing in the morning on a monday, or it might be something else. I have been driving BMWs for roughly 15 years (new ones, leased every 3 years) and there are times I cant get a loaner from them either because they were out. BMW certainly doesnt offer anything else (like uber credits) if they dont have loaners.
Anyway, I certainly cant tell someone how to feel (and am not trying to) but I do find it somewhat amusing how some people that buy teslas act like they bought rolls royces or something.