That may be straightforwardly true for another service — Maps, Email, etc. — but the draw of a messaging platform is its network effect.
"All the freeloaders" is half the reason that WhatsApp is popular: no matter who you want to contact, they likely had a WhatsApp account — from your elderly mother to your college friends to the B&B that you're going to stay at abroad.
If it goes from "everyone I know is on WhatsApp" to "1 in 20 people I know are on WhatsApp" maybe I'm less inclined to continue to fork over $20.
"All the freeloaders" is half the reason that WhatsApp is popular: no matter who you want to contact, they likely had a WhatsApp account — from your elderly mother to your college friends to the B&B that you're going to stay at abroad.
If it goes from "everyone I know is on WhatsApp" to "1 in 20 people I know are on WhatsApp" maybe I'm less inclined to continue to fork over $20.