My impression is that generally plain TeX is used by people who don't like all the LaTeX macro complexity and like to keep things simple (not easy), like to understand better what's going on, build their own tools, etc. In return they give up the ability of using the abundant number of LaTeX packages and standard formatting options, its decades-of-experience code, etc. If you want concrete numbers for a sense of things: on the https://tex.stackexchange.com website, there are currently 179,492 questions (https://tex.stackexchange.com/search?q=is%3Aquestion) and of those 590 have been tagged plain-tex (https://tex.stackexchange.com/search?q=is%3Aquestion+%5Bplai...). Of course these numbers shouldn't be taken too seriously as there are various selection biases in what kinds of people would use plain TeX versus how many of them would ask questions on a site like that, etc.
Interesting, it changes my understanding of tex a bit, as it's not "only" a building block (despite being mainly used as such). Time to follow those links and do some exploring!
Thanks again for the nice answer, people sharing like you did make HN very enjoyable
My impression is that generally plain TeX is used by people who don't like all the LaTeX macro complexity and like to keep things simple (not easy), like to understand better what's going on, build their own tools, etc. In return they give up the ability of using the abundant number of LaTeX packages and standard formatting options, its decades-of-experience code, etc. If you want concrete numbers for a sense of things: on the https://tex.stackexchange.com website, there are currently 179,492 questions (https://tex.stackexchange.com/search?q=is%3Aquestion) and of those 590 have been tagged plain-tex (https://tex.stackexchange.com/search?q=is%3Aquestion+%5Bplai...). Of course these numbers shouldn't be taken too seriously as there are various selection biases in what kinds of people would use plain TeX versus how many of them would ask questions on a site like that, etc.