I don't have research at my finger tips, but shorter paragraphs has long been something that I've heard recommended for online writing.

I seem to remember that people were talking about it as soon as I was working on the web, certainly by 2003 or so. It was described as good usability and maybe there were studies to back that up.

It's more pronounced now on LinkedIn where there is a distinct single-sentence paragraph style that some people refer to as broetry.

Additionally, I think there is a relation to paragraph size and scrolling. People don't want to have to scroll mid paragraph. I notice this with articles that were originally written in Google Docs with a smaller font. They don't read as well on Medium because more paragraphs are getting cut off at the bottom of the screen.