Originally, when Nintendo was porting the Famicom to the US, they…
Originally, when Nintendo was porting the Famicom to the US, they wanted to make it look less like a toy and more like a serious piece of entertainment equipment. So, they made it more like a VCR. Bigger, boxier, and slot-loading. All superficial.
Meanwhile, the original Famicom was much closer to the size of the NES2, the cartridges were also half the size, and it was top-loading.
Japan actually released the NES2 first, as the AV Famicom. Nintendo saw this as a way to backtrack and make the NES more like the Famicom - eliminating the huge flaws of the original NES. However, where the AV Famicom had RCA AV ports, the NES2 did not… mostly because most North American TVs at the time didn’t have AV ports.