I think something had to change eventually. When the 3DS was announced, iPads weren't on the market (so tablets were still a very niche thing) and smartphones were still quite new. In the 7 years since, they've become omnipresent, and it didn't take long for them to become massively more powerful and capable than the 3DS while also being much more portable. I think Nintendo were justifiably worried that if they stayed on their current path, the next handheld wouldn't survive 7 years, just being utterly demolished by phones and tablets. At the same time, the Wii U was a relative failure, and it looked unlikely that they'd ever recapture the audience that made the Wii a phenomenon -- for related reasons, the Wii was an affordable novelty smash with people who weren't big game fans, and that market has all their needs satisfied by their phones and tablets now. So it makes total sense for them to fuse the handheld and console worlds together and focus all their efforts on one platform.
To my disappointment, personally. I wish it were a home console rather than a handheld for reasons that are entirely based on my own needs and tastes (I'll never take it outside so it adds cost for no benefit, the need for portability means games can never really make great use of the motion controls, a lot of multiplayer seems based on the joycons which look absurdly small for adult man hands).