>>13979800
I don't know the specifics of it. I think it mostly has to do with nintendo getting a better grasp on the hardware spec and ultimately consolidating and condensing processing across multiple chips into less and less. There's a few explanations for it, an easily understood one would be additional tampering with a signal is bound to produce more noise. There's RGB bypass boards for this reason, it takes the raw, final RGB signal from a system and amplifies it before sending it out and avoids and low pass filters done by other pieces of hardware.
I guess in the most layman terms possible, imagine a distributed baking process. You have one building that mixes the ingredients. the other which bakes it, and the last one which applies finishes like icing and stuff. There's a distance to travel to each building, and along the way certain things happen that are undesirable, ingredients stagnate, the baked cake gets cold and cracked in transport, and when it's iced, it may not be the cake that everyone wanted.
The SNES is an interesting system too in that its earliest models actually supports the component video standard, Y/Pb/Pr. This was about a full decade before any consumer sets had support for Y/Pb/Pr, and only a few professional sets did (speaking as someone with access to a lot of pro monitors.) You can drill a few RCA outs for a component signal out of the earliest SNES systems. That said I do not know how the picture quality would be on these.