Because half our friends/family/etc own an iPhone and they either use iMessage or WhatsApp, and neither is acceptable for the likes of me. And since they don't

Because half our friends/family/etc own an iPhone and they either use iMessage or WhatsApp, and neither is acceptable for the likes of me. And since they don't 'stoop' to the level of Signal, we can 'stoop' to the level of iMessage (but definitely not WhatsApp).