Nonprofits are more like businesses than people realize: https://seliger.com/2012/09/02/why-nonprofits-are-more-like-... and they pay market rates. Maybe some people will accept someone less for the sake of working at a nonprofit but very few people will accept substantial paycuts over the long term
I've generally found nonprofits pay well below market in exchange for doing social good. Universities are the most obvious example, Chan Zuckerberg Initiative being another