It would be awesomely fun to fly them, but I can't find any. I know there are good old war planes, but no modern ones except for fighter jets. Is there a rule as to why there aren't any? Like it can trigger bad memories in people if they crash or?
No apparent reason. People haven't made any. (And having a rule to ban them because of what happened in the past is stupid IMO)
In my opinion large passenger jets do not have a good "workload to benefit" ratio. I am not keen on simulating airliner crashes not to mention flying around a small map could get boring real quick. Well done static airliners however would be cool for airport maps. My opinion only.
Imho, BeamNg is not made for simulating large passenger airplanes, at least for the moment. What BeamNG does better is simulating metal bending and stretching, which works perfectly for cars, but not for large planes, which are way more rigid and just break into chunks. When making a plane, there are some workarounds that make the plane crashes look more 'decent' than just weirdly bending. Like pre-configuring the plane areas from where they should break, but this approach is not as realistic, though it does the job. Though, as Aboroath said, it is still not a good "workload to benefit" ratio. Ideally, the regions where to 'break' should be calculated on the go, producing different results each time, and even producing some small debris, though this would be a total CPU killer, and that's not how BeamNG works atm, and I don't think it will ever be able to do so in the current node/beams approach. This is not what was asked, but anyway..