Icons in GUIs are commonly used for interactive elements. Most
CLI tools are not interactive, they just produce some output and
the user expects that output to be easy to parse and compatible
with as many terminals as possible.
You can easily output tables, bullet lists and many other things
just with basic symbols supported everywhere. If your CLI
program requires installing fontawesome or breaks in a terminal
multiplexer etc. I'm probably not going to use it.
I merely mentioned fontawesome as one of many possible examples.
And as already said, a symbol having its place in unicode does
not mean it is available on the computer or in a certain
program. For example, in Linux terminals it's not uncommon that
at least one optional font installation is required in order to
get various emoji to display correctly, let alone other non-western
symbols.
Many people use the terminal exactly because it displays fewer
kinds of content than e.g. a web browser, which as a side effect
simplifies many situations.
You can easily output tables, bullet lists and many other things just with basic symbols supported everywhere. If your CLI program requires installing fontawesome or breaks in a terminal multiplexer etc. I'm probably not going to use it.