How do you figure?

Imagine, for a minute, that the spacer is part of the wheel, rather than being bolted to it. So, you effectively have a wheel with less backspacing. How does the hub "know" the difference if the spacer is part of the wheel, or bolted to it? The only thing that should matter is the offset of the hub flange (with no spacer, this would be the back of the wheel mounting surface and with a spacer, it's the surface of the spacer where it contacts the hub) relative to the centerline of the tire tread.

What size tires are you clearing with those 1" spacers?

It's an engineering moment. The weight will always act at the wheel's offset. You take a 1000 pound load at a position at an approach of zero, and you have a near-zero moment. Move the offset out, and you have a 1000 pound force acting at a distance, to create a 1000*dist moment.

I don't know how thick our hubs are. But if you take a 1000lb load at a 2" hub width, you have a 2000 lb-inch moment. With the 1" spacer, it's a 3000lb-inch moment. That's an 84 ft pound difference in torque acting on that bearing. In original form, it was a 166 ft-lb force, that went to 250 ft-lb. That's like torquing a wheel lug at 165lb-ft instead of 110.

My view is this wheel spacers were considered bad mojo for many years because they may cause wheel offset on the axel and an out of balance wheel if the spacer is off a very little meaning vibration.

On the other part any wheel extension will exert more strain on your suspension components and possibly wear them out faster same with very large tires more weight/mass that the suspension has to operate under the faster they will wear out ball joints bearings so on.