The models supplied to Microsoft for PC and Xbox are identical. Microsoft performs some wizardry or other at their end after we have supplied the package. It is up to developers to decide whether they wish to see their aircraft on both console and PC or not - I pick both but some don’t. I’m not sure why.
I can’t really speak to airliners as I don’t generally build them ( Concorde aside ) but aircraft do take a long time to build at any level so I think that it’s just a time issue. They will appear eventually. For now, refer always to review scores in the Marketplace and reviews of aircraft before buying, to make sure you don’t end up with a “dud” 