It's not an OS feature because Apple has an aversion to maintaining any kind of compatibility layer for more than a few years, it's not a third party app becaus

It's not an OS feature because Apple has an aversion to maintaining any kind of compatibility layer for more than a few years, it's not a third party app because Apple doesn't allow JIT code (eg. high performance emulators) in third party applications on iOS. Demand isn't the only reason to make a feature, sometimes customers might want something only after they're given the opportunity to recognize it's value.