IMO, the most important factor for GC not being successful was because of momentum & public perception. They lost serious home console momentum since N64 days. PS2 had stolen the throne by several miles, and newcomer Xbox had put up some great fight against them in the west with good 3rd party support among more older, hardcore gamers. Wii, I think is an exception, because it was able to attract an entirely different audience (casual gamers) - but casual gamers don't really stick around. (Thus, they are casual). By the time Wii U came out, most casual gamers moved onto other platforms like mobile and handheld.
I think of Switch more of an handheld than a console. It's got guts of mobile system, that can be just connected to TV. Many people play Switch purely as handheld (hence, Switch Lite was born). By going hybrid handheld, the were able to avoid direct competition vs Sony and MS with their vastly more powerful consoles, and was able to successfully migrate their core userbase on 3DS to Switch, thanks to the momentum of their strong handheld user base.
For that reason, I don't honestly think Nintendo will make another console that's not also portable, unless something drastic happens in people's viewing habit, or they find a big chunk of new type of audience. As successful Switch is - to me it just feels like they've consolidated their various userbases (Portable/Console/Casuals) into 1 platform... - but will they be able to expand it even further is to be seen - as their eggs are all in 1 basket now, the risk itself is up. Their next step, probably will be quite crucial point for the company, I think.
Momentum is quite important - that the reason PS5 is doing better than PS4 launch also plays the part I think. PS4 launch, they had to do many things right considering Sony struggled the most on PS3 times, almost going head-to-head with Xbox 360 in U.S. Plus, they didn't have BC for PS3, so it was basically like launching a brand new console platform. They had a lot of hurdles, but I think the no-nonsense approach and system's superior power vs Xbox One also helped out. Sony did a lot of things right for PS4, and such success is helping them out on PS5 launch too.
MS had good momentum going on Xbox One - but they lost out eventually, unable to keep the momentum into XSX, which I think is one of the reason that it's not selling as much as PS5. MS, however does seem to be doing a lot of things right this gen, so we'll see how it goes at the end of the cycle. Currently Sony does seem to suffer from some negativity at the moment - will see how they'll turn it around.