Grounds can be weird.
@sunshine_eggo Has some links in his sig. Watch the one with Mike Holt / NEC about grounding. It actually explains it pretty well and clarified some 'why' things for me when it comes to house grounding, and not grounding sub-panels, but it boils down to: You should only have one reference point for above ground devices to (earth) ground. If you have more than one then you have another path for electricity to travel to "ground" which can be dangerous and cause a problem.
Moons ago, doing some testing on a line out to a Hot-Tub with a GFCI breaker back when I was wiring for a pool company I discovered something I always thought was interesting. Drive a rod in the ground, attach a wire roll it out 150 ft away drive another rod, put a meter between the two and you will likely read a significant voltage. But they should both be 'ground' right? People smarter than us have done the research, and they still kind of argue over some of the finer points, but based on Holt's video it starts to make sense when you watch the current flow. Anything that conducts has resistance albeit possibly extremely low, and electricity always prefers the path of lowest resistance. Some electricity will go down the higher resistance paths (see Mr Ohm). Multiple paths can make the electricity double back on the other path.
As an electronics guy, the other thing that always confused was how a portable radio could possibly work since the signal inducted in the antenna does not have a path to 'ground'. Ground is relative. In a radio, or an RV, or any large object ground becomes the most dense thing on the object. So in a portable radio you basically create a ground plane for the inducted signal to reference, with the battery and foil. In a car/rv it's the chassis/frame. Since a vehicle is insulated from earth, it becomes it's own little domain of traveling electrons. I knew a guy with a positive ground VW, I helped convert it. There is another idea that can be hard to truly grok, why that is more better.
