Problems with a single bathroom which includes the toilet:
If you have kids, everyone is fighting over a scarce resource in the morning. Showering/shaving/etc all takes time and you're all leaving in a narrow window.
If you don't have kids the people buying the house may, and they will care. It makes selling the house so much harder.
The bathroom _must_ be cleaned to be guest ready, and they get to accidentally snoop through everything. I love my ensuite for this reason. (and if you don't care about it being clean, your partner probably does)
If you have the room, why not have an extra bathroom? So much easier to build in new construction than add later.
When I lived in Australia the toilet was in a separate room, so the 4 bedroom house worked ok with only 2 bathrooms. The toilet wasn't blocked/held hostage by someone taking a shower. (washing your hands on the other hand...) But this also helped sell the place, since with 2 full bathrooms you can have kids/house mates/etc.
My current house has 3 baths with 4 bedrooms. One is in the in-law suite, which I airbnb, so we have 2 on the main floor. It makes 2 baths for 3 bedrooms. This feels like a nice "adult" house. We have a spare rooms for house guests, and they have a full bathroom they can use. This means we can host friends/family for days/weeks and we can be annoyed by their personality, instead of annoyed fighting over a bathroom. ;)
Of all the weird things in the US, a house having "too many" bathrooms really doesn't seem like a problem.