To fit eight .357s into their N frame S&W had to redesign it so that the barrel is screwed into the frame higher up. Without relocating the chambers further away from the center line of the N frame cylinder the largest .357 capacity possible was seven. S&W recovered their redesign and retooling costs by only offering their eight shot .357s as high priced Performance Center revolvers. It was many years before S&W offered 8 shot model 627s as a production line priced 4" revolver.
At the moment no manufacturer needs to go through the expense of redesigning their products. They can't fill all their back orders as is. So, while I might buy an eight shot RH or SRH because one would be neat, I won't hold my breath until they're on the shelf.
Although I love target shooting with them, objectively, large frame .357s are of dubious value since revolvers are obsolete as duty hand guns and they're too large for concealed carry. For field use, the extra capacity is nearly useless.