so I've got lots of indexed pages that don't get any traffic. What's the big issue?

Moz addresses a critical quality signal issue affecting entire sites when numerous indexed pages receive zero traffic. While Google has never formally codified this relationship, industry experience strongly suggests that large volumes of no-traffic pages send negative quality signals that may impact site-wide rankings. The problem manifests in two forms: thin pages with insufficient content and pages that fail to answer user questions, evidenced by users returning to search results immediately after clicking. This behavioral signal—the "pogo-sticking" pattern where users bounce back to search results—indicates poor content quality or relevance. The concern extends beyond individual page performance to potential site-wide penalties, as Google may extrapolate quality judgments from problematic pages to broader site sections or the entire domain. This creates a compounding effect where low-quality pages don't simply underperform individually but actively drag down stronger content through association. The theory suggests Google evaluates site authority partially based on the proportion of indexed pages that satisfy user intent, meaning even strong content may suffer when surrounded by thin or irrelevant pages that generate no organic traffic.