[halfnormalform]

The solution is to have motion control an ambient light in the bathroom but not the main light. Use a (smart) switch to control the main light and use it when you're going to be there a while. Set up the system not to turn off the ambient light when the main light is on, no matter how much time passes.

This way you get the convenience of hands-free when you're just washing your hands or something, but you have all the light you want--for a bubble bath--or whatever.

There is still the problem of sometimes forgetting to turn the switch off, but since it's smart, it's easy for Siri to turn it off when you go to bed, etc.