Over in sitcom-land they'll do fat guy/hot wife, but don't you dare think about reversing those roles.
The Biggest Loser had romantic subplots that would build throughout the season, too, but the producers and editors made sure to Jim & Pam that s**t as slowly as possible. Those "relationships" weren't allowed to bloom until both partners were skinny enough that their kisses were safe for a presumably very shallow audience that knows love only as something bedazzled on the butts of pretty girls' pink sweatpants.
"Sorry, 'Attraction Can Be Based on Non-Physical Qualities' just isn't cost effective from a glue and rhinestone standpoint."
And no, that wasn't because those couples were only down to clown once they were both skinny. Obese people like genitals and emotions as much as anybody else. It was just the cameramen's sacred duty to make sure as little of that got caught on film as possible. They'd straight up refuse to follow actual couples to catch a glimmer of real romance because, and this was their actual reasoning, "Who wants to see two obese people making out?" If we can stomach watching the oompa-loompas from Jersey Shore drunkenly chewing on each other's faces, we could probably manage a couple of hefty folk gettin' tastefully busy in the bushes.