> My personal guess is that most people use poems to convey sentiments that could best be done via another form (probably an essay or Tweet).

I'm guilty of this. Why? Because I suck at remembering information in the moment, and writing a poem about it makes it easier to call forth from memory when I need it.

For example, if prompted right now about who Karl Popper was I'd just mumble a sentence and that'd be all my mind can cough up. Once I get around to writing some sort of poem about who he was and what he did, I'll be able to talk at length whenever it comes up around the dinner table.