Valve never really tried to compete. Index is old, outdated and never saw a price discount and their supposed Index V2 has been delayed so long it's a huge meme.

HTC never really iterated like Quest did beyond big bulky headsets that required a full room set up did they?

I can't say Meta spending 10s of millions to push the technology forward is monopolistic unless you want to say Nintendo, Sony and Microsoft consoles or any device with a walled garden (ipad/iphone) ecosystem is monopolistic.