Probably a safety feature. Say somebody breaks into your car when it’s parked outside, hits the button and gets access to your garage and potentially house.
I found this a bit different as well, but I am changing my habits to work with it this way. It is a more secure approach.Is this the case? Set up homelink garage door remote opening with buttons under rear view mirror. Works fine from outside and inside of garage when car is on... but nmot when it is off. Very inconvenient. Is this your experience? Is there a way to override this limit?