I think it is a trend that started with sales emails. If you see sales emails from mailing lists, you might notice they tend to be structured like that. Supposedly because they want to capture people who have short attention spans who are averse to reading paragraphs of text.

But articles on Medium are not sales emails.

The opposite is also bad for online articles - paragraphs that are too big. When I was doing my part time job managing a website for an educational charity, they would sometimes send me articles to put on the blog. I often had to break up paragraphs that were too large. They were used to academic writing, which is often written in that way. But large paragraphs like that are too big for the web.

The way you have written your article here is perfect. Paragraphs of about three or four sentences are ideal.