Well, IIRC, PMDG tried to release the DC-6 for Xbox. And that failed so badly that they pulled it from the market, gave refunds, and said it was never going to be on Xbox again. AFAIK, this remains the case today, 2 years down the road. I don’t know about the 737 as I’m not interested in that plane.
But let’s be realistic here. Undeniably, the Xbox has limited capabilities compared to a gaming PC in many different areas. Some of these areas require special code, another limits texture resolution, and seemingly others require dumbing down the code and thus limiting what can be simulated because the Xbox can’t keep track of as many variables and/or threads as a PC. I don’t know the specifics as I’m not a programmer these last 15 years or so but I know enough about the subject to understand the problem. But anyway, playing MSFS on Xbox is not going to give optimal results in a lot of cases.
So, look at this from the perspective of a developer wanting to deliver the highest-quality product possible. Xbox forces you NOT to make the highest-quality product possible, at least for that platform. Thus, you have 3 options. First, you can NOT make the product for Xbox at all and put all your (probably limited) amount of dev effort into making the PC version all it can be. Then you hopefully get rave reviews from the PC audience but get no revenue from Xbox at all. Second, you can ONLY make an Xbox friendly version which will work on PC. Then you get Xbox revenue but your reviews on the PC side will not be great and your reputation might be damaged as a result. Plus, you’ll have to sell for a lower price because the quality will not be as high as it could be on PC. Or third, you can make the best PC version you’re capable of, then pare it down for Xbox, if this is even possible (apparently it’s not for things like the DC-6). Now you have to support 2 distinct versions and you might not have the resources to do that, PLUS work on your next release. As a result, I’m not surprised that some devs, who take pride in their work, go for the 1st option, PC-only as good as they can make it, and ignore Xbox.
Really, Xbox is like an old PC, never capable of seeing MSFS in all its glory. This isn’t a slight on Xbox users (nor old PC users), it’s just the facts of life. If you want all that can be wrung from MSFS, you need a good, newish PC. Thus, IMHO, the decision to release MSFS on Xbox was so it could serve as a “gateway drug”. Xbox users who liked it enough, and realized that their experience is limited by their hardware, would then buy a PC so they could get all the goodies.