Why would anyone do that?
@JeffThePilot because we can't be experts in everything and you'll always find a builder to say it's okay. Even apparently reputable ones - just look at the scandal over cladding on blocks of flats.
I had an extractor hood over my hob which looked great and whooshed when I switched it on before I realised it wasn't on an external wall and there was no flue so it was just for show. I've had the kitchen redone and haven't bothered with a fancy stainless steel hood because I have only one external wall in the kitchen and that's already taken up with the sink, washing machine and boiler. I just open the back door if it's smoky and repaint the kitchen every year.
You find the same with internal bathroom extractor fans that make the right noise but don't actually vent to the outside. And cladding outside tower blocks. We think they look nice and assume they must work because otherwise people wouldn't be allowed to install them, would they?
A lot of builders will say it is okay to have a Saniflo or machinator toilet (shit muncher) as a secondary to a properly plumbed in primary loo. But in my experience there are always problems because the system can't cope no matter how careful you are with what you put down there.
I might have an ensuite if I could connect it to the existing sewage pipe or have an external wall where I could install a new one. But for me it would be a faff and a waste of space.
My bathroom is on the landing next to my bedroom - same as many people. There's a solid wall between them and two doors and proper plumbing. It's no hardship to get up for a wee in the middle of the night, nip to the bathroom and flush the loo and jump back in bed. I prefer it to using a loo behind a door in part of my bedroom which is better off as a wardrobe and listening to the noisy motor run and the extractor that goes nowhere running for 10 minutes.