Signal used to be an SMS (text message) client in addition to its secure IM protocol. If both people were using Signal, it would use the secure protocol, otherwise it would fallback to a text message. They removed the text messaging feature from Signal and now it's a lot harder to convince normies to use it.

Previously: Hey replace your texting app with Signal, if two people use Signal you'll be upgraded automatically.

Now: Hey use Signal, no one you know is on it and you'll need to remember who uses SMS and who uses Signal.