To my knowlege there is no practical way to automate placement AND routing of a PCB design (so basicaly only the a netlist as input). Yes, there are autorouters, but they work under the assumption that there is already a sensible placement of the compontents. Is this still true?
At least Mentor Graphics & Altium don't seem to have any solutions for this.
Not sure if it's true, but SparkFun's platform still appears to require manual design, just it looks like their staff will do it for you. To test-drive it I selected an ESP32 with a humidity/temperature sensor, and it quoted a board cost of ~$35, with a one-time ~$1k design fee.
So presumably they give the component list to a real human who does the board layout for you.
It can be automated if your requirements are limited and your expectations are low. I think that's the approach SparkFun are taking here -- aside from power, the only connections needed are between the components and the microcontroller, so placement is kind of arbitrary, and they leave themselves enough room that even a terrible autorouting job will work.
