As someone who has recently gotten into the research world, I read a lot of preprints and occasionally dig up some technical reports to access older publications.
To me, it seems like technical reports were the paper version of preprints. Many technical reports appeared later as peer-reviewed articles or chapters of books. Nowadays, there are far fewer technical reports appearing. My department used to produce multiple dozens each year in the 70s and 80s, but they have only produced one so far this year.
Does this mean that preprints have taken the place of technical reports? Is there any reason why a researcher would choose to publish a technical report with their university or organization?