WhatsApp also had no need for moderation or ads handling (IIRC, they used small yearly payments plus contracts with network operators). Just handling the ads,

WhatsApp also had no need for moderation or ads handling (IIRC, they used small yearly payments plus contracts with network operators). Just handling the ads, both backend and user interfaces for buyers, would quickly net you several more developers. It's easy to have only 45 engineers when you constrain the scope of what they have to do very well, but the scope was much, much, much smaller than Twitter's.