Pre-1940 earnings data?

Does anyone know why no pre-1940 earnings data? Do the data exist, but no extracts?
Tom Hirschl

The 1940 census was the first to ask questions about income. You can find more about income and employment questions in the 1940 census in this national archives blog post. IPUMS does provide the variable OCCSCORE (standardized as a z-score in ERSCOR50) in pre-1940 samples, which for respondents with an occupation, reports the median total income of all persons with that particular occupation in 1950. Please refer to this user note for more information about these and other measures of occupational standing.