Justified by who?

I am not speaking as a consumer here. I am speaking as a devils advocate which I feel like you are missing maybe.

I am not saying I agree with what I am saying. I am explaining why a situation may not result in what you want happening.

If there is no FINANCIAL benefit perceived by the publisher/company management to fund ongoing development and merging of work performed to create the xbox build in with the steam build, there may not be the ability for the developer to do so because of lack of funding and support.

My argument was never one of "ability" but "financial feasibility from the viewpoint of the bean counters".

If it takes 3 months of full time work of multiple developers to port those changes over, lots of companies aren't going to sign up for that no matter how much "good will" it might gain them. Those steam sales are already sold. There's no financial incentive to update the game for those people, especially if you can get them to buy the better version elsewhere.