with almost 3 years on the market Switch has surpassed Xbox One in global sales and whether sales will rise or slow down after PS5 and Xbox launch is still a question but the Switch is clearly a Winner for Nintendo.
Many thought the Switch would be another WiiU and be dead at arrival and some still believe the Switch is just another gimmicky fluke.
There are many reasons for the Switchs success but I think the top 3 reasons are
the most obvious, Nintendo did a terrible job with marketing the WiiU and thought the console would sell just by having the Wii name on it. It also didn't help that they were very strict with youtubers promoting their games around this time and by releasing two versions of the same console at launch first it confuses consumers and the 8gb model would require you to buy another harddrive with more storage anyway which costs even more than the 32gb model making the 8gb utterly pointless.
2. back to core audience
the Wii/DS era was and will probably always be Nintendos biggest success story in history but Nintendo had a huge focus on its casual audience with games like Brain Training, Nintendogs and Wii Sports, Fit and Music which were very innovative and fun for a while but games for the core audience was overall a wasteland other than the standard Nintendo games which are incredible.
Nintendo tried this tactic again with the WiiU and they utterly failed because they actually believed that the casual audience would be just as loyal as core gamers and would stick around for the next Wii Fit well nope. Casuals had moved on to smartphones and tablets and Nintendo was slapped back to reality that their core audience are what made them successful in the first place and were under appreciated for years. Admittedly, Nintendo tried to balance both audiences with the WiiU but it was just far too late and too naive of Nintendo to think that gamers will blindly support them without giving us a good reason to buy the WiiU and funnily enough most WiiU games have been ported to the Switch now which definitely has a more core gamer first mentality which goes to my final reason.
1. the games
Nintendo has proven everytime that they don't need the most powerful hardware to make good and innovative games. The WiiU is a big failure for sure but it has some incredible first party games that is what kept Nintendo relevant all these years even during their worst moments and with Nintendo promoting their games so much better with Directs Mario, Zelda Smash Bros sales have reached new records and even lesser known Nintendo games like Xenoblade are seeing more success and recognition.
Sure Switch has lots of ports but it actually helps to have some than none like WiiU. More 3rd party games are seeing ports on the Switch and while they may not be as succesful as first party games it's a start which Nintendo has to keep going with their next generation of consoles. Nintendo has done a good job with the Switch, again we still don't know how it will hold up against PS5 and Xbox which might end up being another Wii situation but this time Nintendo can act on time and release a more powerfull version of Switch which probably won't match the other consoles but will keep them competing like they should.