I would say that backpacking is not so much about "simple" as it is about "light" for the obvious reason that ounces equal pounds and pounds equal pain. The selection of gear is heavily influenced by size and weight constraints primarily for that reason. There are some pretty skookum pieces of backpacking kit that really aren't "simple" per se, but they're light as a feather. In vehicle dependent travel, overlanding, the size and weight constraints are greatly reduced, which allows the comfort factor to increase. I would argue that backpackers are not into backpacking so much because they love to walk, but because they love to explore the majesty of creation and get away from the pressures and noise of modern civilization. The physical fitness/exertion part of it may be one aspect - they like the challenge, for example - but ultimately it's not the main point, or they'd be better served just hitting the gym and running on the treadmill.
Likewise, I would argue that overlanding is driven by the exact same core desire to explore, to find wild, hidden places that few are able to see, and witness the beauty of creation first hand. By using a vehicle, our range is massively extended and we can get to places that would be utterly impossible to explore solely on foot. The technical off road driving aspect of overlanding is a ton of fun, and many including myself enjoy it immensely, but again, I think I speak for most here when I say it's not the main point for us.
As for "light on the land" - the tread lightly mindset is a core value of Overland Bound, so I would say the majority here have that covered.