Development got really slow. Developer was tangled up in some small personal issues.

I guess you're being humorous, but it was a completed and widely used system. IIRC it was default for Slackware (which I guess was quite niche).

Reiserfs wasn’t quite complete - if it got heavily fragmented, you had to backup, reformat, and copy your data back.

Unfortunately ... if you let it ride much above 80% disk usage for very long (or less time the fuller it got) it would fragment bad and the performance just fell off a cliff bad.

SUSE had it as default as well. Quite sad that it was tied so much to the main creator's personality and "private issues" kind of sealed the fate of it. :-(