I went there just now and posts have like 20-30 comments on most stories or around 100 on older, popular threads if you click "load more stories". I remember when it used to have hundreds of comments per post.
I was a Slashdot regular for around 10 years. Then somewhere around 2008/9 I realized that almost all of the stories appearing on the /. front page had featured on this new site called Hacker News days earlier, minus the random trolling and "frist post" spam. I briefly used both and ended up switching to HN entirely. Still my daily source of tech news.
The proximate cause was that the owners didn't put in enough money to keep the site good. The ultimate cause is that there isn't much money to be made advertising to techies, so it's not worth spending much on.
It's surprising how little money there is in advertising to a tech audience, considering that we buy a lot of discretionary stuff personally and influence many billions in corporate IT spend. But the only tech sites that manage to make a few bucks on advertising are product review sites or shallow mass-market journalism like Wired. There's a lot of money to be made if you can figure out how to monetize a tech audience.
I made quitting slashdot my new year's resolution for, hmm, 2001 or 2002, give or take?
Not that it was terrible, it just seemed to me to be a huge timesink, and many of the stories were a bit sensationalistic / click-baity (anti-Microsoft, or about some kind of flamewar).
Looking back... I guess it was ahead of its time, like a social media / algorithm before we had those, and later the whole internet became like that :(
TL;DR: mismanagement after the original and subsequent sales, an outdated editor and link/summary model, and a migration of relevant users driving discussion to other areas of the Internet.
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I am a 4-digit UID user of Slashdot starting ~1997. I was a regular and active contributor up until 2006 or so and then sharply curtailed my contributions as a commenter as other sites became far better at offering recent/relevant news and conversation with me eventually switching over to Reddit (until their CEO became anti-contributor) and then HN.
Long ago, it was THE place for relevant nerd news and discussion, but throughout the various sales, ever-eroding userbase, lack of serious updates for mobile users (don't even get me started on how I still need to use the Desktop site because the mobile version just...sucks), and lack of keeping up with better front-page moderation/editing, it became clear that other sites out there were providing a much better UX for 'nerds' on 'stuff that matters', especially moderated content and conversation.
Today, I find something interesting on there once a month or less and instead head here, daily, to find relevant links and useful discussion about content that 'matters'.
Unless something changes at HN (see Reddit, Digg, and/or Slashdot), I don't see any reason to move away from HN; this is simply the best (for me) when it comes to surfacing interesting tidbits, stories, and interesting stories. While I do miss the good 'ol days of Slashdot, it's become like every other Internet dinosaur--a dying relic of days gone by because they refused to capitalize on their userbase FOR their userbase, instead opting to capitalize on the userbase for money, instead.
Slashdot died several deaths.
The birth of Digg and Reddit were a big contributor (as was HN later). You may also remember that /. was sold, first to VA Linux, then to another company, along with its sister, Linux.com.
Slashdot's model of editor selected stories also meant that the number of stories per day was lower.
The editor selections when CmdrTaco left, along (slowly) with other editors such as Roblimo (RIP) and others changed the site's feel.
It's clear the Slashdot product is kept around but not actively developed. Many sites from that era are in much the same state, or shut down entirely. RIP Freshmeat, kuros5hin, and others.