This applies to basically any too-expensive-for-most-people live performance genre. I'm pretty sure the Met can fill every seat for every performance if they price things correctly. That's a bit complicated, of course, because we are talking about price discrimination (soak the richie riches, sell the leftovers at a discount to the less rich). But I don't think it's that complicated. In any season there are probably some superstar performances which will sell out, or at least close enough. But otherwise, I'd guess attendance isn't that hard to predict. They can reasonably guess there will be 200 empty seats or whatever. Get rid of rush tickets, which involve uncertainty and waiting, and change it to a lottery where people know by noon or whenever that they have a discounted seat. The miracle of phone apps can make this work. Distribute discounted tickets as a standard practice to university student activities office. Show up at 10AM, get your tickets, if no one does throw them into the lottery pool. Anyway, the point is to engage in price discrimination in ways which don't make it too inconvenient for those who pay the cheaper prices. I get rush tix at my local orchestra occasionally, but it isn't exactly convenient. Turns a two hour evening into a 5 hour one. I don't always have 5 hours to spare.
I used to go to the Met occasionally because I knew someone who had a line to discounted tickets. They still weren't cheap, but they weren't sold for crazy prices. But I can't afford to pay the standard rate, and nor can most young people (I no longer am) who might be the future audience.