Your question is also kind of like asking why HP laptops are lower quality than Apple laptops. Emirates uses its Dubai base to serve primarily lucrative international flights, just like Apple targets the premium end of the market. That doesn't mean that HP is in a market segment without competition, however. Rather, it targets a cost-sensitive portion of the market where people aren't willing to pay extra for quality.
It's not as though the US air market isn't heavily protected. You'll note that foreign carriers like Emirates can't fly domestic routes. If I fly Qantas to NYC, half the plane gets off in LA and nobody else can get on. Which is part of why "Qantas ticket" is the ancient Yolŋu word for "financial ruin".
So why can I choose to buy either an Apple laptop or an HP one in the US, but don't have the choice to fly on Emirates from Chicago to NYC? I think you missed my point entirely. There is a market of people willing to pay for superior quality airline service, there is just no supply for it, because of regulation.
They're agressively seeking to increase profit margins.
That meant that expensing has stripped away the ability to book business class tickets. (That is arguable if that's a good idea or not given the complexity of tickets)
The aggressiveness about seeking higher profit margins at all costs has also meant that the money that would be available for those things are considered to be "fat".
The closest that you have with the Singapore/Emirates setup is United Polaris and Global Services.
Please tell me you're joking.
Are they though? How come the US doesn't have the equivalent of a Emirates/Singapore quality level airline? You can't tell me there is no demand for that level of service by business folk?
Laymen's explanation - there are a limited number of routes that can physically be established and those who have the routes exhibit rent seeking behavior with only just a small amount of competition. In other words an oligopoly.