Originally Posted by
Adam Smith
You're right. So where exactly in the economy cabin did it have its lavs?

Il-18 then
Jokes aside, I think ultimately down cost and space. It isn't technically impossible to tap into the existing line already running along the fuselage from the FWD Lav/galley to the holding tank.
However, if you're putting a lav near row 25-27 on the A320 or just behind the J cabin, you can't exactly put 6 seats back in the rear bulkhead.