Eh, Half Life 3 is just a meme at this point. It's impossible to make it and have players feel satisfied because they will expect the new coming of Gaming Jesus.
They're too happy and lazy getting rich from selling other people's games on Steam. They're not going to bother doing anything requiring more effort than more random shitty hats.
I heard that we'll never see HL3. I don't know is it truth or not, but one Valve employer said that there were a lot of prototypes of HL3 but no one was accepted. Valve just don't know how to do HL3 becouse it's overhyped and if they'll fail it'll be a disaster for their reputation.
It was already confirmed in an anonymous interview with a valve employee that hl3 straight up doesn't exist. Its been started up as a project a few times, but never got off the ground.
I agree with what you said about HL3. just wondering how many of the young gamers even know what the whole HL3 thing is about. Also https://developer.valvesoftware.com/wiki/Valve_Time