It's because although the work is done by hand, he can eventually (in like a month) hand it off to his own employee or contractor for them to do for a fraction of the profits.
Starting it up himself allows him to formularize the entire business, build a following and keep costs low in the beginning. He probably also plans to start creating similar email lists for other verticals with high levels of contractor work - so not just developers, but also designers, devops etc.
If you read between the lines, you can see where he's going with this; it can absolutely be a passive income stream, and based on his traction, it may replace his need to work.
Edit: To commenters below - Most successful businesses eventually hire someone to run them w/o much intervention from the investors/founders. He can do the same.