why do you think half-life 3 mysteriously never comes out?
Why didn't they though?
To be honest it IS wierd given the hype this series used to have. It's the strangest decision ever made by any company i can think of.
Perhaps some key people left and Gaben & friends were uncertain they can pull another Half-Life with new people. Because they could make an average shooter with some gimmick (like HL2 was) and it would be a bestseller. On the other hand, maybe their plan was to make Alyx, make Oculus popular, and then make HL3, but the plan failed.
One more explanation i can think of is simplier and therefore more probable - money.
Valve makes shitload of money on zero-effort work such as skins to CS2, their MOBAs and other shooters. HL3 would be a bestseller, but it's a singleplayer game, you won't sell many skins there. It's better to focus all the work on multiplayer games with skins everywhere and on everything, this generates enormous amounts of money.
CS2 is free, or you can purchase a 'premium' (aka, you play with other premium players only) for only a few dollars on a sale. Similar with DOTA2. And yet they are always on the 'bestseller' list on Steam because of all the microtransactions. It makes more money than Cyberpunk, BG3 or Ghost of Tsushima, best selling but only singleplayer games that don't sell skins.
Gamers are literally retarded.