It's ridiculous to even consider this in New York, where they could have just been building normal apartments instead of luxury condo towers for the last 10 years.
Price, mostly. Luxury amenities are a consequence thereof.
However you can't just blame it on demand. These are $16 million condos we are talking about. Functionally they are entirely different goods from apartments intended to be inhabited as a primary residence by people who are not extravagantly wealthy. Moreover, vacancy rates for luxury apartments were high before Covid, and remain high now, even while the rest of the city continues to deal with brutally low vacancy rates in all other housing categories.
So the situation is a little more subtle than "low supply, therefore high prices" and warrants further scrutiny.