They are the sellers of a VR headset, and want to increase the odds of that market taking off by adding a great game to it. Business decision wasn’t based around the game’s ability to sell well, but it’s ability to sell headsets. While this one game isn’t going to get me to buy a Vr headset, enough games at this level could, and there 100% are people who bought the headset just to play Alyx.
Which isn’t to say that Alyx could have been made as a non-VR game, from what I know VR is completely integral to the experience. But in choosing to make a different game that could have sold gangbusters vs making this game to support their hardware, they chose the latter.
Edit: Oh also they are so loaded they can do whatever they want basically and as a private company have no authority to answer to that can force them to pursue profit. I get the feeling Gaben is entirely happy with his current level of ludicrous net worth and values seeing a big change in the landscape of gaming in his lifetime over making more money. (It’s also possible that attempting to make new markets for Valve to take a 30% cut of is the best long term strategy to make money regardless)
I had thought the same, until I actually played it, and then it made complete sense. It's hard to express how difficult it would have been to have designed a non-VR counterpart with it until you're in the game experiencing it -- the pacing, the environments, the Combine, etc. I feel it's completely different than any Half-Life game, or FPS game that I've played, but familiar at the same time.
As far why they did a VR game at all: I suppose they like to test the waters.
This is my own analysis, as a Valve veteran for 20 years and someone who has followed every twist and turns. People will say they made this game to sell VR headsets, but from my vantage point, it's the opposite. They actually created VR mostly for Half-Life.
In one part, HL games were always a place for innovation and pushing the gaming boundary forward. It may have just been fun games to you, but HL1 defined storytelling in FPS games, and HL2 defined physics puzzles and grand landscapes. Each game was better than the previous and eventually they got stuck no being able to make something they were truly happy with.
Valve has always been more satisfied creating something new than more of the same. They experimented with a lot in the past decade. They tried making a horror game with biometric sensors, which did not work but lead to the Steam Controller. They tried a lot more things but VR finally fit the bit. It allowed them to partly sidestep the "perfect game" issue, by switching into a new area that wasn't yet explored and allowed for innovation again.
So yes, they made a VR game because they are once again able to push gaming forward and create a truly unique game, which is the only way they will be satisfied enough to release a game.
EDIT: just saw your reply below. I hope you get through it. It is GOTY for me.