I'm sure Valve wanted to make a AAA VR game to help sales of their hardware so they made a new Half Life. Rather than they wanted to make a new Half Life game and then decided to make it VR.

Valve's games generally push the envelope WHEN they write games. They don't do what a lot of game developers do, which is, make games, improve gfx, rinse and repeat. Valve likes to walk in the room with something ground breaking and will knock your socks off. VR is the next logical step and it needed a nudge. I think Alyx is that nudge.

Although I won't be able to buy it for a while due to hardware expenses, I really applaud them in going the VR route. Personally wouldn't have done a prequel. This would have been a perfect HL3 fit. I'd love to hear why they chose a prequel to HL3. Buuuut, what's done is done and I'm sure they did a great job.