I wonder why Ping or WhatsApp wasn't able to get this viral. The only viral feature I saw is when I installed it, it went through my contact list (I'm assuming)

I wonder why Ping or WhatsApp wasn't able to get this viral. The only viral feature I saw is when I installed it, it went through my contact list (I'm assuming) and found all my friends that already have it installed. Others were able to find me even though I didn't enter my phone number when signing up. Weird.