* sub-par user experience: WhatsApp is just nicer and smoother, and people tend to like that
* very few people understand that Signal DOES NOT get your full contact list, while Facebook (through WhatsApp) does
Especially the second point is very relevant with the current situation — you do not necessarily want to expose your entire social graph to Facebook. But so few people understand this, and even fewer grasp that Signal can still work without doing the same thing.
Ive used both for a while and WhatsApp is aweful, at least on iOS by all standards I can find. Signal feels like iMessage with reactions, voice recordings, and handy tools. WhatsApp feels dated, clunky, and for groups it gets very very messy fast with out reactions.