This is expected behaviour. There are a lot of features that are active on the vehicle even when the key is turned off. The vehicle is always in standby.
If you do not have the plan to use 450 for some days or going on vacation, then it is good to ‘Shutdown’ the vehicle.
Exactly the reason why the 450 has a vacation/Shutdown mode built into it. With this feature, you can turn your vehicle off with a tap on the dashboard. Once in this mode, the self-discharge is substantially slower and the charge should last over a month. To disengage the vacation mode, you can simply put the key in, and the vehicle will turn back on.
However do note that if we were to completely shut the vehicle off when the key is removed, access to those parameters will get cut off. Add to that, the vehicle will need to initialize and boot up every time the key is used, which will take a longer than expected time to start up. Something that can be an annoyance if someone is using the vehicle on a day to day basis for city commute(which is the predominant use case for the vehicle).