Why Is The Airbus A350-900 More Popular Than The A350-1000?

The Airbus A350 XWB family represents an exciting development in next-generation long-haul air travel for the European manufacturer. It first flew in 2013, and entered service with Qatar Airways two years later. The family consists of the A350-900 and -1000 variants, of which the former has seen far more commercial success. But why is this the case?

This is a companion discussion topic for the original entry at https://simpleflying.com/a350-900-vs-1000-popularity/