Given the type of both recent and predicted conflicts that the US has been involved with, it's not 100% clear to me that the US needs yet another aircraft. That is, fighting in proxy wars or fighting in countries like Iraq, Afghanistan, or Syria don't need anything new. And fighting a sophisticated enemy would probably ramp up to nuclear deterrents and diplomacy anyway...fighters wouldn't make a notable difference in…
If there is no specific credible enemy to fight, there are no strict reguirements that MUST be met, so one makes the plane do everething, because you dont really know what you need.