There are two big reasons why hiring altruists still makes sense in many cases:
You don’t have any alternative candidates worth hiring, or finding such a candidate would require a large investment.
A particular altruistic candidate looks sufficiently better than the alternative candidate that the difference between candidates exceeds the difference between the altruistic candidate’s value at your organization and their value elsewhere.
Another consideration for hiring an altruistic candidate is that altruistic candidates are more open to lower salaries which then makes it more likely additional hires can be made.
Encouraging altruistic workers to self-subsidize altruistic work is a dangerous path to go down, in my opinion. On a large scale, it can (and does!) put downward pressure on sector-wide wages, which in turn can push qualified people away from the sector (thus hurting the talent pool), disproportionately may exclude people of humble backgrounds from getting jobs in altruistic work (which in turn helps ensure that people of privilege are over represented in those jobs, which is not good—e.g. this post), and may also, according to some sociological theories, possibly lead to a societal devaluation of such work (e.g. what is seen with care work, which also is bad). I’d much rather let such people seek normal wages, and then donate the excess—you get the same benefits, but avoid all of the associated problems.
Another consideration for hiring an altruistic candidate is that altruistic candidates are more open to lower salaries which then makes it more likely additional hires can be made.
Encouraging altruistic workers to self-subsidize altruistic work is a dangerous path to go down, in my opinion. On a large scale, it can (and does!) put downward pressure on sector-wide wages, which in turn can push qualified people away from the sector (thus hurting the talent pool), disproportionately may exclude people of humble backgrounds from getting jobs in altruistic work (which in turn helps ensure that people of privilege are over represented in those jobs, which is not good—e.g. this post), and may also, according to some sociological theories, possibly lead to a societal devaluation of such work (e.g. what is seen with care work, which also is bad). I’d much rather let such people seek normal wages, and then donate the excess—you get the same benefits, but avoid all of the associated problems.