IMHO, anonymity takes a certain amount of unavoidable effort. If you're just chatting with friends, maybe you really don't need Signal. If you are whistleblowing a large corporation or a government, then it makes more sense?
Carrying car keys (or a fob)
House keys.
Wallets.
IDs.
They all require some mental effort.
If anonymity was a factor, and not ease of use, they’d never only allow phone numbers as login.