I'm not sure how complicated the logistics are, but I am surprised that US airlines don't offer more "order ahead" meal options domestically, mostly for first class, but even for coach pax at a price. Looking at an airline like AirAsia, passengers have about 20 choices including many that are allergy and vegetarian friendly, and while I don't have any data to say for sure (there is no direct nutrition info, but you can sort of guess which items are high/low in fat/protein/carbs), quite a few seem to be on the healthier side, especially compared to US meals.
Also, just opinion, but I don't feel that food *has to be* high fat/salt/sugar to taste good at 39,000ft, but airlines are responding to passengers' tastes. There are two things going on here:
1) I believe that most Americans' taste buds are conditioned to expect high amounts of those three things to begin with, even on the ground, so while airlines might need to put *more* of them in to get the same effect, it's not JUST the altitude. I think that vegetables and fruit largely taste the same, and as long as chefs use a *slightly* fattier cut of meat (chicken thighs vs breasts, for example) that won't dry out too much, a lot of extra fat/salt/sugar does not really need to be added to whole foods for them to taste the same as they would in a healthy form on the ground.
2) I would guess that many people "splurge" on planes, so they don't care as much about what they are eating. Yeah, they might skip something like a jell-o salad with whipped cream on top, but for a high fat/salt dish like fettuccine alfredo, most people are going to look at it and say, meh, it's only this one meal. Of the people who would look at both fettuccine alfredo and the fatty cut of steak with mashed potatoes while on the ground and say "wow, both of these are unhealthy, I want neither," some likely just apply a "cheat meal" in the air, so there isn't enough left to convince the airlines to change.
It should be obvious that the US Majors don't want to cater. They have decades of history to draw on, a fickle audience (in many ways), and now understand there's no upside, and little incremental revenue. One only has to look at the commercial success of Southwest to see this in action. It seems likely that domestic ops will find a natural "market equilibrium" where no catering of any kind is an established norm. Though I think its crazy that transcon length and longer flights are going/gone to that model, unless something unforeseen changes, it looks as that's likely. It possible the next gen of aircraft could be specialized enough for these routes as to not account for things like ovens and greatly reduced galley space, so that full pax catering isn't possible (not even optional order ahead).
The rest of your ideas I find hilarious
No one is "splurging" on a plane (maybe a few in premium, offered genuinely premium fare... not the US4); people are simply hungry, and this is there only option. Its not a "cheat meal", its the "only meal". Many fliers don't have the luxury of time ahead to dine in terminal or bring their own, for a huge variety of reasons.