There's two models that solve this.
a) sell support contracts
b) have contributors sign copyright agreements, license the project as GPL/AGPL, and then sell commercial licenses for people who can't use that
a) sell support contracts
b) have contributors sign copyright agreements, license the project as GPL/AGPL, and then sell commercial licenses for people who can't use that
which seems to be by far the most common
Selling support contracts is actually hard.
GPL/AGPL preclude widespread adoption (these days) — the grandparent explicitly mentioned “permissive” licenses.