I agree. I have an Aventon Level2, and it's tires, 27.5 x 2.3. are fine for both road and gravel, and I'm big guy, and often commute with two full panniers.

Ebike tires under 3" wide have stiffer side walls and casings which help smooth things out, and avoid punctures. They are meant to have more pressure so they can bear the additional weight and speed. More than 3" is overkill. Fat tires trade off performance for looks (which you mentioned, and I agree they look cool)

Fat tires (wider than 3") pros and cons.

Pros: bigger contact patch (especially on lower diameter tires) = better traction, more comfort at lower PS, especially off road , flat resistance.

Cons: more rolling resistance hurts range and efficiency, awkward steering in tight corners or low speed, and the extra width/bulk is a real pain in daily handling — loading on a rack, hauling up stairs, squeezing through doorways, fitting in a car. On an already-heavy ebike, fat tires will have you muttering, "what a pain in the ass."

Unsprung weight (the wheels) are the single biggest factor impacting performance. Ebike wheels with motors in them are bad enough (which is why mid-drive is better). Unsprung weight is why cycling enthusiasts spend 1.5 to 3K on wheels and carefully consider tire and even tube weight. Downhill MTB tire width is typically around 2.6". These bike often exceed 28 MPH, go insanely airborne, and smash into roots and rocks, etc., and 2.6 has them covered. Why would ebikes need more than that? You have already answered that question - people like how they look.