* 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.
The full contact list is uploaded to Signal servers by the phones. The only protection layer that users have is the questionable security of Intel's SGX.
It's still much better than what WhatsApp is doing, just not a black and white situation.
To add a point to your list: Signal does not have automatic cloud backup of messages, unlike WhatsApp. On WhatsApp, 30% of users have cloud backups enabled [1], meaning that you can basically assume that any reasonably sized group's messages can be accessed by people who have subpoena-power over Google (chance that there is no backup-enabled account in a group of n people is (1-0.3)^n... for 6 people it's already 12%).
Yes, it's hashes of phone numbers instead of the phone numbers themselves, but that's a detail. Phone numbers are easy to brute-force especially for people the protesters are worried about, as well as easy to build rainbow tables for.
If they were all individually salted, there would be no way to compare against new joiners.