TLTR: Lack of good content, and amazing alternatives.
- Huge backlog: I used to track 2k+ blogs on Bloglines/Google Reader, it was nearly impossible to read everything, but the collective mind of the internet made easy to keep track of what my close friends were reading using delicious and I could easily keep up with good content.
- Lack of good content: Once delicious was losing interest, I started to rely on Twitter to find good content, again unsuccessful. Thanks, today we have Reddit/HN to filter this, but getting a click from HN won't make me "subscribe."
- Good alternatives for tech content. Today most conferences dump their entire collection on YT; I'd rather watch a 45mn lecture on 2X on youtube or listen to an excellent podcast than read a long blog post.
- Audibooks =)
In the long run, it's almost impossible for individual text blogs to compete with such social validated content and curated content.
edit: typos and grammar