Actually, Labo already sold through its original shipment by the end of last year in Japan. Retailers there have just recently ordered more. The facts still remain, Labo sold well for its first year, and Nintendo will march forward with it whether you like it or not. Also, local store sheves are not a good indicator for a game's success. My local Best Buy had stacks of unsold Smash Bros. Ultimate copies, that game surely must've been a flop /s.
Yes, I was part of the crowd who expected this thing to be an instant phenomenon. But that was mostly personal hype talking. It was only after learning and reading about Nintendo's intentions for it that I adjusted expectations accordingly. Still doesn't change the fact that it did well.
Adults do have a lot of buying power, but adults aren't all hardcore gamers. The Switch appeals to a wide array of consumers regardless of age, taste and gaming experience.
"The retailers sold their initial shipment 8 months after the release" is exactly the definition of a flop. Initial shipment is supposed to be the initial sales, not the first year sales. You can say that the numbers are not that bad, but the fact that they sold in 8 months (after price cut) what they expected to sell in the first weeks shows enough.
And Nintendo pushed Labo a lot in Japan, at launch you couldn't go anywhere without seeing it, and you had special staff in the stores to hype it and push people to try it. Even for months after launch, you had a huge ad for it in Akihabara (maybe it's still there, didn't check lately). They put a lot of efforts and marketing into this thing, took 8 months and the holidays to sell the April launch shipment, and you think that "it sold as expected" and "It's pretty good"?