A door has two states to choose from, so having a door covers all use cases.

And a third type, people who have had children so have gone through the toddler stage where a toddler would literally chainsaw and burn down a locked door before they let you have 3 seconds of peace to take a shit.

I would be surprised if private defecation is not a majority preference among couples.

Even if I'm alone in a hotel room, I'd prefer to contain the odor to the bathroom.

We tend to not care for showering/peeing, but pooping is something else...

I’ve actually ended otherwise decent relationships early because the other person was way too coy/upset with bodily functions like farting and pooping. If we’er sleeping together I expect us to be farting together. And if we are living together I expect us to be using the toilet in front of each other. Anything less is both inconvenient and reflective of deep personality conflicts that will never be resolved.