This is bike shedding. The nuances of which principles to use to convert notebooks to standalone apps are complex with unexpected trade-off, so instead you prefer to focus on the borderline inconsequential point of the format.
This is also similar to the header formatting for Weave.jl, markdown for Julia.[1] This is probably also inspired by R markdown, but I mention it because it seems to be a reasonably common practice in tools for the data science field.