Why are PhD posters a thing?

There is a trend afoot, encouraged by the funders of research, to ask PhD students and other academic researchers to design posters explaining their work. The aim, I think, is to provide an accessible means of explaining (often unfinished) academic work.
It’s a nice idea, but many of the posters end up unattractive, overly technical and uninformative. Sometimes, they are designed to cram all the contents of a PhD on to a piece of paper of around one square metre. When that happens, they end up illegible due to the huge amounts of tiny writing. More...