Traditionally all electric systems required a good number of batteries which brought with them weight and the need to be charged. The rule of thumb was you did not use electricity for heating and cooling given amp draw. Having propane on board takes care of heating and for most truck campers a 2,000 watt genny can do battery recharging plus run the AC. Mine weighs 45 pounds.
Since you mention AM Solar, I knew Greg Holder, the founder of AM Solar pretty well since he and I spoke at Life On Wheels conferences and he used to refer customers to me on occasion to assist with their solar installations. If you ever saw his Winnebago motor home which was his rolling test bed, the entire roof was covered in solar panels, however, he still used to say when choosing between a generator and solar, go with the generator first as it provides the most flexibility with the least expense. In the example above it strikes me that 400 pounds of batteries plus an inverter is not able to do what a small genny does costing $1,000 or less.
It is not that you can not make an all electric camper. That has and is being done, as Mike pointed out. It does not come cheaply however or else requires adjustments to lifestyle. As with all things RV, you can have anything you want, if you are willing to pay for it. For a good many folks, dollars still weigh heavily in component and camper selection:)
Steve and Andra
2012 F350 6.2 gasser SRW LB
Fab Fours front and rear in case we run into a rhino
2019 Northstar Laredo SC