When exporting a feature class in ArcMap from the Table Of Contents, the subtypes and domains associated with the feature class are not maintained.
This is by design. When a feature class is exported from the Table Of Contents in ArcMap, the underlying geodatabase configuration is not carried forward with the feature class to the geodatabase.
A domain declares acceptable attribute values in fields. Attribute domains can be shared across subtypes, tables, and feature classes in a geodatabase. A value which is not in a domain is not accepted in a field.
Use the Feature Class To Feature Class tool to convert the feature class to a geodatabase feature class. The Feature Class To Feature Class tool maintains the domain and subtype settings.