To be more specific, they added this fee in response to a NYC regulation mandating a minimum $22.13 for delivery workers. [0]

There is debate about whether or not Doordash needed to do this, if they are just being vindictive etc. But what we do know is that regulation came at a cost to NYC consumers. And it wasn't just Door Dash. Uber Eats added a $2 fee and Instacart added a $5.99 fee. New Yorkers can determine for themselves if they want to pay higher prices to ensure higher wages.

[0] https://about.doordash.com/en-us/news/changes-to-fees-nyc