I believe it was due to AOL and CompuServe forums, which were most importantly, new, novel, friendly and easy. Technical people were "above" AOL and so those Usenet communities survived a few more years, but ultimately succumbed to web forums which were superior to Usenet in almost every way.
Unfortunately, web forums were mostly hollowed out due to social media, and now that people are sick and tired of that, the simplicity and "innocence" of early 2000's forums, and even 90s Usenet, seems appealing (although tinted by rose-colored nostalgic glasses).