Because most of a CPQ scope has to be asked, not read from the system. The whole risk of the project is the bundle, rule or approval nobody mentioned in discovery. Be obsessively thorough in Blueprint — the product and pricing spec is the artifact that is never scoped tightly enough.
Produce two hard deliverables before build: the product and pricing spec (every product, bundle, grouping, price and discount rule) and the config blueprint (rules, validations, approval flows, post-contract motions, billing and contract-length handling). Engineering builds to that map; anything missing from it becomes a change order.
Every claim above comes from work LeanScale published. These are the sources.