Non-profit does not mean charity, though it can. If the non-profit is well funded then there's not necessarily a reason that employees ought to make direct donations via their paycheck.

None of which is to say that a particular individual might not wish to take a position with a particular non-profit that pays less than market rate for a variety of reasons. Only that non-profits often pay full market rate for development [in the context of donors] and fund-raising and administrative staff as well as for services and goods from outside organizations.

Good luck.