Not only is a space and money issue with a lot of people, it's a time issue as well. It would take me well over an hour to clean each of my one-gallon tanks, but now it only takes me half an hour to clean my ten-gallon. One filter, on heater, three fish. Yes, I am worried about one of the fish getting through a divider, but my 175lb boyfriend had troubles sliding my dividers in and out of their slots, so I doubt a little 2 ounce fish could knock it down.
I know you said your fish prefers to be in a bigger tank, and that is true of some fish. Some prefer bigger tanks, some prefer smaller. Though given time, I'm sure your fish would adjust to a smaller tank if the need be.