It's off-to-the-side of your main point, but AOL Instant Messenger shut down in December 2017. Per https://www.technologyreview.com/2017/12/14/67582/aol-instant

It's off-to-the-side of your main point, but AOL Instant Messenger shut down in December 2017. Per https://www.technologyreview.com/2017/12/14/67582/aol-instant-messenger-made-social-media-what-it-is-today/ https://www.technologyreview.com/2017/12/14/67582/aol-instan... it was down to 500,000 active users a month the summer before it was shut down.