The FHIR Specification states that default values are only allowed in logical models, which limits their relevance and use in many IGs. Even within that narrow context, it suggests that they should be used sparingly. From an implementation perspective, our experience has shown that implementing auto-population of default values would likely be complicated, and similar behavior has been confusing to users in the past. Given that absence of a value is semantically equivalent to presence of its default value, we do not feel that the added complexity of specifying this behavior justifies the small return on investment it would provide. As such, we do not plan on implementing such a feature.