They’ll never release HL3. They are not a developer anymore. They are just a game store/directory. HL3 has been overhyped so much that anything released would be a disappointment. The gaming market has changed too much from when they made a game engine and released half life to showcase that game engine.
I can probably list a million more reasons why they’ll never release, but those are the big points.
Half-life Alyx was HL3, just it was better to name it not HL3, because fans would lose their minds.