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)

They aren’t exactly worth nothing. If you have too low karma (in a subreddit), your comments will be hidden etc. I uttered an unpopular opinion in a sub once, got downvoted to oblivion for it, and since then every single one of my comments is hidden. You always need to carefully judge how many unpopular opinions you can say in a subreddit until your karma falls below the threshold.