I don't think Moxie insists on this. I remember reading this on the Signal blog[0] a few years ago:
> Social apps need a social network, and Signal’s is built on the phone numbers that are stored in your device’s address book. The address book on your device is in some ways a threat to the traditional social graphs controlled by companies like Facebook, since it is user-owned, portable, and accessible to any app you approve. For Signal, that has meant that we can leverage and contribute to a user-owned portable network without having to force users to build a new closed one from scratch.
> However, many Signal users would also like to be able to communicate without revealing their phone numbers, in part because these identifiers are so portable that they enable a user’s conversation partner to contact them through other channels in cases where that might be less desirable. One challenge has been that if we added support for something like usernames in Signal, those usernames wouldn’t get saved in your phone’s address book. Thus if you reinstalled Signal or got a new device, you would lose your entire social graph, because it’s not saved anywhere else.
> Other messaging apps solve this by storing a plaintext copy of your address book, social graph, and conversation frequency on their servers. That way your phone can get run over by a car without flattening your social graph in those apps, but it comes at a high privacy price.
> I’ve been trying Element (from Matrix), but its UX is quite poor. I just wish chat apps would copy at least some of the UX of Telegram.
I think Signal may be trying to copy some of the UX features that drive people to WhatsApp and Telegram, while maintaining the security. Adding stickers and stories with e2ee is probably quite the challenge and maybe less challenging than a creating secure solution, especially connected to the cloud.
I personally am grateful they're adding more features and agree, would love for Signal to add UX elements at the rate of Telegram. BTW, I don't think Telegram has stories, which is a feature I really love on WhatsApp, so I think if Signal has that, it may be easier for me to get people to switch to Signal.