Nintendo Switch has had one of the best selling dynamics in a long time. Why do some people still think that the console will not exceed 100M units sold? It is already at 66M units sold in 3 years and 9 months is huge, the PS4 had taken 3 years and 11 months to reach this score. The Switch is a primarily portable console and Nintendo are just unbeatable in and dominating this industry.

100M is a huge milestone. Only like 6 systems has ever done it. Cant blame people for not automatically think one will.

Mainly because Nintendo consoles seem to hit a wall hard ll of a sudden. This is partially Nintendo's fault as they abandon the console and don't continue to make games and focus on the next.

Wii at one stage felt like it was tracking to hit 140 million, then suddenly sales died.

The escalating perception of low quality with Joy Con drift issue? Fans already talking about Switch 2?
Threads like this defensively challenging low estimates rather than focusing on solid outlook? You tell me.
As you say, Nintendo are in non-competitive niche of their own, so nobody not engaged with it really cares.

People aren't good at predicting sales. 100m is a given at this point, even if 2020 is its peak and declines notably each following year.

Because Nintendo likes to kill off consoles early.
As someone already pointed out, the Wii was selling very well and Nintendo just happened to announce WiiU and not release any more big games for Wii. Wii sales then fell sharply.
It all depends on Nintendo. If they start releasing Switch 2 in 2022 and their games won't support cross-platform, then Switch might not get to 100 million sold.
Wii sold only 5m in all of 2012, which was the year WiiU came out (November 2012 to be exact).

IMO it probably will reach 100m but not more than 120m.

Yep, in the past, Nintendo needed to refocus it's Software efforts towards its next system and had to do this while balancing Handheld and Consoles software lines & hardware launches. Switch has resolved this issue until a successor is released since it has combined Nintendo's software output. 

With the Switch, past trends are really out of the window. The Switch will not perform like prior Nintendo systems in its price bracket, so any illusions about falling off a cliff or slowing down are a bit of wishful thinking from people. Next year will likely see hardware sales that rival this year's, and the Switch is yet to have an official price cut, Switch Lite being a somewhat of a price/feature cut(similar but more successful than the 2DS). 

Some people underestimate it because they are only interested in Nintendo failing. 

I'm hoping Nintendo advances on its platform and releases a Switch 2, rather than replacing it with a dead-end "new Switch" or some unrelated new platform.

Just because Apple and Samsung already do this thing with their own devices doesn't mean it automatically isn't something Nintendo should do. In fact, this model is something people have wanted in the video game industry since the Master System and Mega Drive.

Agreed. In the past, in order for a device to do well in its final year or two, Nintendo would essentially have to sacrifice the first year or two of the next system by keeping the current one going with software. 3DS had a terrible launch lineup in its first 6 months on the market, for example, because Nintendo probably focused on making too many first party DS games releasing in its final couple years. I suspect with this unified approach that they will still be able to pump out a decent amount of games for Switch 1 during its last 1/3 life, while at the same time preparing plenty of launch software for Switch 2.

But as I've said in other threads, something that is working against Nintendo can only be understand by looking at their history. Development teams in other companies are constantly pushing hardware, and that hardware is constantly upgrading. PS1, PS2, PS3, PS4, and PS5 all have huge power gaps (even if graphical improvements haven't made as huge of a jump as they used to. Same with the xbox consoles. Developers working on those devices have been used to these jumps for decades now, every 6 years or so. What about Nintendo lately? I say lately because they have changed their focus in recent generations.

DS to 3ds was a big jump, and 3ds to Switch was arguably the biggest jump for any device ever. GameCube to Wii was an extremely tiny jump. Wii to Wii U was massive. Wii U to Switch was extremely tiny. I still can't really tell a difference between Wii U and Switch versions of the same game. To me, the Switch feels like a portable Wii U, and a 3DS on steroids, which is alright with me.

What's my point? Nintendo in recent gens usually pushes themselves on a device, followed by another device running on a similar level. I know they do this to keep products around $300 or less, rather than $500 like the other two companies do, but it doesn't allow their dev teams to constantly stay up-to-date with the latest hardware technology. They always make games that look insanely impressive on the tech they are using, but that's because those teams more or less stay on the same power level for 10-12 years and so get REALLY used to using it and optimizing for it. Wii U was a rough start, so I suspect Switch 2 could have a rough start as well as I predict it will be another massive leap forward for them and it will take their teams years to get used to it before they really start working efficiently. Switch 3, I predict, will have more or less the same hardware as Switch 2, but with some revolutionary new design like the Wii was to the GameCube or the Switch was to the Wii U.

And where exactly do you meet these people? I think everyone on this forum these days believes the Swiitch will sell more than 100 million.