Me: "Humans are bipedal"
You: "Some humans have only one leg"
Also, nitpicking, but you can dance even with just one leg, as the first (or one of the very first) verses in "Moving to Florida" by the Butthole Surfers shows ;)
What you're missing:
Source: I play for dance clubs as a musician (they usually use recorded music, but will hire a band for an event such as their annual ball).
The costumes in the pictures you'll only see at a competition event, but people still dress up for the club dances.
The community of these people is not large, and they know each other, and will network to find a venue to meet up at.
It's really too bad more people don't do it. The barrier of learning it is rather high, as there's a long awkward stage, and few are willing to put in the effort. But the payoff is lifelong, and as I wrote, it really dials up the pleasure from music.