First things first, i'm not sure if Labo will be a major success, one thing being the overall pricing, especially if you include a Switch. Another one being how long it's appeal will be lasting.
But, there are multiple points that are really pro Labo.
Mass appeal: Let's be honest here. The typical forum dwelling core gamer actually is the one out of touch. We've proven it multiple times over the years. At least with concepts that aren't for the core audience.
Labo is attracting to many people. Sure, kids who see the Labo video and like any kind of creative work or handicraft like stuff actually love it. They're really curious what they can do with Labo and how. Parents who wnat their kids to not only play on the screen really like it. Adults that might not even be into video games like it and want to know what you can do with Labo. Basically everyone who is into crafting and the not digital only ways of playing thinks it is great.
Bait: Yeah, somehow people already came up with 'Nintendo wants you to break your console and buy cardboard over and over again'. Now, cardboard can not only be very robust. It's pretty easy to build your own spareparts in multiple ways. Let Nintendo sell their replacement cardboard. But they took a material that can be surprisingly riggid and at the same time easy to replace. As for LAbo destroying consoles or the joycons, i haven't seen anything that points in this direction. Sure, it might happen. Also might happen that someone accidentally pulls his PS4 from the lowboard while playing PSVR or accidentallyhtrows down his tv and stuff like that.
Cashgrab: Producing Labo as a final product might be relatively cheap. But there was creative and inventive work done, there will be advertising costs and all that. Labo isn't neccessarily cheaper than other games. You even can't sell it digitally in the same way as other games. And, even if people now like or even love it, the whole concept is so far of from traditional gaming that it could (have) become a total flop. Especially after the toys to life wave just faded away. Labo could still be a straw fire. Even if preorders seem to be good.
Honestly, i think some are just pissed of that 'shitty stupid cardboard' get's such a mass appeal right now while stuff they like doesn't. At the same time many core gamers have a big blind spot on gaming related things with a real mass appeal.