A 30 amp plug has one hot or power wire that feeds electricity for the entire 5th wheel. A 50 amp plug has two hot or power wires that feed the 5th wheel.
So based on what you are saying the RV designers wired what they considered the basics to the one wire that would have power if you had to use a 30 amp adapter cord at the campground. You will still be able to operate the slides and have hot water. Again just what the designers considered the basics.
The missing second wire is what powers all the rest of the comfort items in the coach like the AC, microwave, television etc. Once you get back to a 50 amp hookup the rest of the 5th wheel systems will come back to life.