When I saw the October reveal trailer, I knew the Switch would be around for a long time and would be a massive success. It was the natural evolution of Nintendo's Handhelds and Home Consoles in one, so yeah I thought this would be a 100M seller at least. They get to have all their teams on one device and that really helps with software output and I still don't think we've seen the full extent of this just yet.
An actual post of yours from March 2017 had you predict 50-60m lifetime.
While this may look like I am specifically picking on you, you merely happen to be a concrete example of a guy who posted in this thread and has a memory that differs from reality (multiple old threads got bumped today and your old post happened to be in a stack of quotes on the final page of the thread I lifted your post from). The topic that people may be misremembering their own predictions has been brought up in this thread here and I am sure you aren't the only one. Hence why the poll in this thread doesn't seem representative of reality at all.
Your 50-60m prediction looks bad in hindsight, but at the time you made it, you were still on the optimistic side of the spectrum, so there were a ton of people who made worse predictions.