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.
Then digg came along, and I started using that, but kept Slashdot on the backburner. One day I remember listening to a diggnation podcast, one of the live ones with Kevin and Alex in front of a live audience at (probably) some bar somewhere, and Kevin made a remark about "Slashdot effect.... it's the Digg effect now!" and the crowd roared.
And he was right. It had been a fair while since Slashdot had managed to take anything down.
I felt a little sad, for a moment, because I knew what it meant.
Initially, the aggregation was only part of it-- the discussion was the best part. By the time Slashdot Video started happening, the comments had already gotten a bit 4chan-esque. I consistently saw comments rated "3: Troll" or similar because people were just using upvotes (without any specific descriptors) to counter what others had downvoted as obvious troll comments. Last time I went back, I looked into the comments to see pages-upon-pages of ascii art swastikas and just thought... why the hell would I bother with this?
The lack of moderation over there probably started as a philosophical stance that, at that early, naive juncture in the internet, I sympathize with. I'm guessing that after that, it just became a cash cow that they didn't want to bother creating an FTE to manage, and now most of the remaining users are there solely because it's a community that rewards being an obnoxious edge lord spewing out content-free insults as long as they resonate with the obnoxious majority in the comments.
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'm not even clear who owns it now. It would surprise me if it's very profitable.
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 :(
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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.