Less duplication, but these are most-commonly used as field codes (field datasheets, checklists, banding codes, etc.). With standardized common names, most people don’t know all the scientific names for each North American bird. Codes based off the common names are easier to keep track of because they can be sussed from the names used (I say “there’s a morning dove” when birding with a group of people, not “there’s a Zenaida macroura”).