[the_af]

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.

[shmerl]

May be, but mechanical difficulty adds to less usage too.