It really fell off the rails when it became an imageboard moreso than a forum and link aggregator. It was all about the text, and so attracted those most willing to tolerate a wall of text.
Use Archive.org to compare 2008 to 2010, 2012, 2014, 2016 and onwards. The addition of thumbnails and gradual shift of the frontpage away from textual content and towards images is almost as remarkable as the increase in high-anxiety, anger and tribalism.
At some point sub-reddits were added, as well, which probably didn't help with the tribalism.
Use Archive.org to compare 2008 to 2010, 2012, 2014, 2016 and onwards. The addition of thumbnails and gradual shift of the frontpage away from textual content and towards images is almost as remarkable as the increase in high-anxiety, anger and tribalism.
At some point sub-reddits were added, as well, which probably didn't help with the tribalism.