Later in the post: "The only exception came among self-published authors, who saw book-related income almost double since 2013. Despite this uptick, self-published income levels remain 58 percent lower than traditionally published authors." and "Amazon controls approximately 85% of the self-published market and so most self-published authors have no options other than to accept Amazon’s non-negotiable terms."
"The respondents reported a median author income of $6,080, continuing a sharp decline over the last decade: $8,000 in 2014 and $10,500 in 2009 (per the Authors Guild’s 2015 Survey), down again from $12,850 in 2007, as reported in a joint Authors Guild/PEN survey.Authors Guild Survey Shows Drastic 42 Percent Decline in Authors Earnings in Last Decade | The Authors Guild
Earnings from book income alone fell even more, declining 21 percent to $3,100 in 2017 from $3,900 in 2013 and just over 50 percent from 2009’s median book earnings of $6,250.
The survey showed a shift in book earnings to other writing-related activities, such as speaking engagements, book reviewing or teaching. Including those sources, respondents who identified themselves as full-time book authors still only earned a median income of $20,300, well below the federal poverty line for a family of three or more."