Explicit versus implicit feedback — why does production almost always run on implicit?

Explicit feedback is a deliberate rating: stars, like, dislike. Implicit feedback is behavioural residue: clicks, dwell time, purchases, repeat visits. Explicit is scarce (a few percent of users ever rate) and skewed toward extremes. Implicit is abundant and free, but has no negative class: a missing click means "never seen", "not interested", or "seen but not now", and the log cannot tell them apart. Implicit signals are therefore modelled as confidence in a positive, not as a rating.