I imagine they do sell more than a few over time, but if Yamaha ever released their sales numbers by model, I bet you'd find that this is one of their worst selling models. What it does have in its favor is that it's probably already paid for it's R&D costs, it fills a niche in their lineup for a heavyweight adventure bike, and they sell just enough of them to make it worthwhile to continue production, at least until they're forced to meet increasingly strict emission standards. Why do you think it hasn't received any kind of makeover since 2014? Because it generates just enough sales at its current price point to keep the line going, but not enough to devote funds for any substantial upgrades. Also, any upgrades would raise its price into closer competition with more expensive models like the GS, or the Triumph Tiger, or the KTM 1290. If buyers didn't swarm to the bike at it's $15,900 price tag, why would they suddenly pay $20,000, when other bikes in that class have far more built in status and sex appeal? If someone is willing to pay big bucks for a toy, they're going to want a toy that makes people go "oooo, aaaaah" when they see it. BMW's do that. KTM's do that. Triumph Tigers do that. Super Teneres, not so much (except when someone momentarily mistakes it for a GSA).
It IS a heavy bike. For a 2014, It's claimed curb weight is 584 pounds; once you add all the accessories that we all install, it's 600 plus pounds. The fact that other ADV bikes are heavy doesn't make this bike less heavy. The fact that the message was delivered by a Harley guy riding a 900 pound Barca-Lounger does't make it less true. It's very heavy for a bike that you plan on using for single-track, or hucking over logs (which is kind of the way they marketed is as that "go anywhere, do anything" sort of bike). It's definitely heavy if your planned ride is going to involve picking it up multiple times a day when it falls over downhill. That Harley guy probably would have said the same thing if it was a KTM 1290 sitting there, or a GSA; it just happened to be a Super Tenere.
As for making fun of fat Harley guys, come on....have you ever looked at the trip photos that so many of us post on here? We are an old and portly bunch ourselves. HD bros don't have the market cornered on double chins or big guts (and I include myself in that description).
This bike is a wonderful machine. It's a top notch touring platform, it's as reliable as gravity, and I love it more than any other bike I've owned. It's great on highways, gravel roads, dirt roads, and anything else that could reasonably be called a "road". It's also a chunky beast that shouldn't be anyone's first choice for their planned Darien Gap crossing.