You're right that there are many messengers available and Signal will, at best, be one of many that people juggle based on who they are contacting. That's why

You're right that there are many messengers available and Signal will, at best, be one of many that people juggle based on who they are contacting. That's why it was a huge advantage that, on Android, Signal could replace a SMS client. You weren't adding _yet another_ messenger to the list, you were replacing the SMS client with one that could send secure messages. That made "switching" to Signal (which, ofc, was not a switch at all for my friends who use SMS) much easier for me. I could continue texting my friends and seamlessly switch to secure messaging if they ever got signal. Contrast this with my friends who kept their old SMS client who reliably forget to check / use signal and generally tend to go back to texting me in a few weeks. Even if you send 0 signal messages for a long time, by switching you SMS client you are already setup to receive them and will habitually open an app that supports E2E encryption. For example - Facebook Messenger also supports sending and receiving SMS messages - likely because they've done the research and found it drives adoption.