I don't think it's because they are mechanically difficult to use as you imply, but rather that they are subtler or more nuanced symbols than most people know h

I don't think it's because they are mechanically difficult to use as you imply, but rather that they are subtler or more nuanced symbols than most people know how to use. A lot of people are comfortable using the dot, the comma, and maybe exclamation marks. AI-speech seems to strive for more formal writing by default.