They support them with Hardware and technical resources. Seeing what happened with the whole CentOS mess, I am kind of glad that homebrew remains independent and can continue to do so without relying on Apple’s money.
Apple is invested into MacPorts (and also pays several employees working on it).
To be fair, I think the number of employees specifically paid to work on MacPorts is probably zero. The ones that do work on it seemingly do it in addition to their regular duties.