Again, it's in Oculus' business interest to have their SDK extended to cover HTC and Valve headsets. And, again, if the Oculus SDK was extended there'd be no need for SteamVR apart from people owning WVR headsets.
As to why Oculus haven't extended the SDK to cover WVR headsets nobody has a clue. What we DO know is that Valve aren't giving Oculus permission to extend their SDK to cover HTC and Vive headsets, perhaps Microsoft have done the same thing?
And of course Oculus would want HTC and Valve headsets to be covered by the Oculus SDK, it would effectively DOUBLE their potential consumer base. Your arguement against this makes no sense whatsoever. If Valve and HTC headsets could use the Oculus Store natively the owners of those headsets would be attracted to those Oculus Store exclusives and purchase from there without needing to worry about the Revive developer getting run over by a bus or something
Nothing would change for Oculus headset owners on Steam, everything would change for Valve and HTC headset owners on the Oculus Store. Oculus would have the benefit of attracting more headset owners to their Store, Valve will have the disadvantage of having a competing Store with top quality exclusives. And then it will come down to which Store has the best prices, which is a win for headset owners.
And then of course you'll find developers starting abandon the Open SDK, something that Valve have spent A LOT of time and money developing, because using the Oculus SDK will increase performance.
It's in Oculus' business interest to extend their SDK, it's NOT in Valve's business interest to allow Oculus to extend their SDK. Them not giving Oculus permission to do so is anti-consumer and anti-competitive, and they don't get anywhere near enough grief for it.