This is not about moral philosophy, but practical matters. Tor's anonymity depends on diverse ownership of the running relays. As it stands, the organizations accepting donations to run Tor relays (torservers, noisetor, etc) already control a sizeable chunk of the total relays, and that's why the Tor project would rather encourage people to run their own.
Of course, many people can't or don't want to run an exit node. In that case, it's much better to donate to those organizations than to do nothing. But the Tor exit relays are not soup kitchens, and increased security for the Tor network due to more diversified operator group is not easily convertible to a dollar value.
The underlying hardware of the provisioned nodes would still be under the control of easily-bugged machines in large datacenters from the perspective of government level actors.
Of course, many people can't or don't want to run an exit node. In that case, it's much better to donate to those organizations than to do nothing. But the Tor exit relays are not soup kitchens, and increased security for the Tor network due to more diversified operator group is not easily convertible to a dollar value.