That's probably because the rider is not likely to survive a catastrophic frame failure at speed. If you do a
Google Search a number of fairly alarming pictures come up. Even if it is fairly rare a catastrophic failure is going to be, well, catastrophic and it is worth the time and effort to avoid it.
If you shop around, there are a fair number of e-bike brands and models that have substantial weight ratings. Also most any e-cargo bike will easily carry your weight. With a few exceptions, most e-bike frames are rated from 220-250lbs of rider, and there is enough slop in the design that you should be fine. if you don't ride down flights of stairs or off of high curbs you should be fine.
My other suggestion is that you have a good relationship with a local bike shop that can periodically inspect your frame. Even the very best frames can accumulate damage over time that can lead to catastrophic failure. This is exponentially more true for a folding bike or for a full-suspension mountain bike, and you should be somewhat more concerned about step-through designs as opposed to full diamonds (which are a lot stronger). Have the bike shop inspect the wheels while they are at it.