I think I have like 90 games of lux in recent memory.
You're only HALF correct. Support mains would play lux because they want damage potential (and the potential to "carry" by being this stupid high damage burst machine)
But they're probably not playing it because of autofill. Anyone who gets autofilled into support doesn't have enough experience with support to hop onto the role as a mage. If they do, then there's no need to complain. And if they don't, then they'll pick a generic support that everyone knows about because they don't know the role enough to do anything else.
It would probably be more likely to see an autofill support playing Thresh, Blitzcrank, or Nami or something rather then a specialization support.