> Any reason they can't be installed trivially?

Capsule size. The last I saw the pod designs, passengers are all reclined cockpit seats that aren't going to have a whole lot of elbow-room, let alone any chance to stand. "Holding it" is an option, but it caps trip time at an hour or so. Past that you're going to be hosing down an awful lot of capsules.

Every (non-local) bus I've ever been on (Greyhound, Megabus, BoltBus, smaller local companies, etc... I've been on a lot over the years) has had a bathroom.

Every design I've seen of the hyperloop had people seated with no provision for facilities. I am assuming there are engineering reasons for it otherwise it logically would've been included.

And of course it is different from a bus. If a women is pregnant or violently ill on a bus you can stop at any time. And in fact every Greyhound bus I've been on will stop at various gas stations for toilet/food/drink breaks.

It's worth mentioning because what good is the technology of hyperloop if the economics fail (because no one will use it).

Every greyhound bus I've been in has a tiolet in the back, maybe not the most amazing experience but it sure beats pissing into a water bottle.