Lots of good points. Xbox is a big factor in this. Also, this was around the time many millennials were starting to buy consoles on their own and Nintendo was seen as somewhat childish. The more mature games were coming out on the other consoles at the same time that the first generation that grew up with pervasive gaming were becoming adults.
I was such a millennial. Disappointed by the game selection (and perceived childishness) on the N64, I wound up with a PlayStation. Then I went with an Xbox for the next gen, followed by a Slim PS2. I did buy a Wii but owned few games for it. I basically skipped the Wii U era altogether.
I got a Switch on launch, but it was the same thing within a couple of years: I wanted a console with better performance because many of the best games of the generation would not be on Nintendo’s platform or would be ported years later with worse graphics (and with the premium of the Switch tax). I have a fairly big library for the PS4/5 while my Switch sits unused.
I still very much appreciate Nintendo’s own games, but a console needs more than first party titles.
