Nintendo obviously wants to make money. However, if making money was ever the impetus for online services, it would have charged a subscription fee all the way back on DS. I think Nintendo viewed online as a simple feature so it offered it for free. Then, the realization set in that having online and doing it well were entirely different things. Servers and maintenance cost money. The no frills connectivity for online matches that Nintendo has offered for over a decade probably wasn't setting the company back a ton.
Eurogamer ran an article a few years ago wherein a developer stated:
At some point in this conversation we were informed that it was no good referencing Live and PSN as nobody in [Nintendo's] development teams used those systems (!) so could we provide more detailed explanations for them? My only thought after this call was that they were struggling - badly - with the networking side as it was far more complicated than they anticipated. They were trying to play catch-up with the rival systems, but without the years of experience to back it up.
I'd imagine once Nintendo finally researched this and decided to expand its online features, it realized it couldn't realistically offer a robust online service without charging.
I've played very few games online on my own hardware. Mop it up and I played Resident Evil: The Mercenaries 3D for a couple weeks a few years ago, and that was the most I played a single game online ever. Regardless of Switch's subscription fee, I can probably pass. I doubt I'd use it enough to justify it.