I am a tech nerd over 30, using a mixture of windows and linux, and watch porn. While I’m not a furry, they have great art IMHO so people can share it even if they aren’t 100% into it. Some of it might even be ideologically driven, against the anti-porn drive: Add a lot of good porn content so that in case e.g. Reddit shuts down NSFW there is a good alternative.
No, it’s because WhatsApp was free at a time where SMS were not (you might have a few included in your plan, but you couldn’t rely on that)