No one I know uses WhatsApp either (thank fuck). No one wants to download another app that now they have to juggle between different sets of people. I’m a software dev and even I hate all this nonsense of ten different messaging apps. On any given day I might use slack, discord, Zulip, Google messages, imessage, and matrix. Two is too many, this is just ridiculous. Absolutely no one in America wants to be using this many apps to communicate. Which is why most people just use the default.

I'd argue that Signal is the cleanest and simplest messaging platform out there

If anything, the complicated thing might be that the data is stored locally on your device, so you need to take extra steps to back up the data

But every platform has some small quirks to learn. People figure out how to adjust to all the other "big" platforms because they want to use them. It's not that Signal or Fediverse is harder, some people will use it as an excuse to feel justified in not switching