In the mid-19th century, American sanitarians came to believe that disease stemmed from “sewer gas” emitted by toilets, which encouraged home builders to cram tub, sink, and toilet into one well-ventilated room with exposed pipes, in order to limit the spread of disease. While the sewer-gas theory would be overturned by the science of contagion, the three-fixture bathroom remained a staple of the modern American home. (Elsewhere around the world, the toilet is far more commonly found in its own chamber, separate from the bath.)
That doesn’t sound like the most plausible explanation for the 3-in-1 trend, but I clearly remember how everyone combined toilets and bathrooms into single rooms in the nineties in Ukraine.
On bathroom remodels:
According to Zillow research shared with The Atlantic, a simple bathroom remodel—such as replacing the toilet, adding a double sink, or tiling the floor—carries the best bang-for-buck of any home renovation. At $1.71 in additional home value for every $1 spent, it’s three times as cost-effective as a kitchen renovation.
As always, Hacker News has an interesting discussion.