For one, we like very loud movies and video games at all hours of the day and night. I don't think that would be great for them. Plus I have 5 cats & a dog that would probably just be nosey sometimes.
Mostly though everything is so much easier when they are in their own space. Cleaning the cage, letting them out to play, feeding them. I never have to worry about the other pets getting to them or them escaping & hiding somewhere.
We're currently homeless and staying with family, so the rats are in our bedroom...along with 3 cats and a cockatiel. It's manageable, I clean the cages every few days and scoop the litter multiple times daily. No more incense or spray perfumes, and the window can only be open when it's hot out.
Mine are also in the living room. They get so much more attention that way. But I have three kids under five and it can be very noisy to say the least. Plus the cage is in direct view when you open the front door and I know someone is going to be unexpectedly forced to face something out of their nightmares haha. I was just wondering whether that was a factor for most people.