Long Story short - you need external Code do make nice but sophisticated things on Mod.
For example you will have on the DC-6 an “virtual” Co-Pilot. This doenst work on Standard Flight Sim Installation. But due injecting your own line of codes in the Mod, the Devs can do things which are normally not supported by the standard SDK of Flight Sim.
That is the reason, why “Study Level” Planes are today not available for Xbox like the DC 6 or the Piper Warrior from Just Flight.
And this is also the reason why the most Xbox simmer are very hot to have this kind of update 