I think it mostly happened when HN became flooded by Reddit users. One of the reason I think this is because of how HN and Reddits way of dealing with new lines is different. In a lot of the comments on HN that I would consider to be fitting on GPs point you’ll see a format a long the lines of this:
This is the first line of my paragraph.
This is the second line of my paragraph.
They are separated because HN and Reddit formatting is different.
I think that's because people are commenting on mobile, where the lines are way shorter. What looks like a paragraph on my phone (e.g. this comment), turns out to just be a line or two.
This is also how 4chan differentiated users, by double space and ironically using >greentext wrong. I thought it was ironic to see this comment here, because, I've been using the old 4chan archives as datasets for interesting things. https://archive.org/details/imageboard_datasets
This is the first line of my paragraph.
This is the second line of my paragraph.
They are separated because HN and Reddit formatting is different.