"Back in 2012", Django was already 7 years old and had taken most of the market share of the first generation of Python web libraries and frameworks. This included that strange beast that was once considered the "standard" Python web system, Zope. Bluntly, Django had a much better development experience overall than the older web options.

(Mind you, the likes of Zope and CherryPy are still out there and under development. You just don't hear about them much.)

Up until about 2010, web dev in Python was converging hard on Django. It took Flask and similar small frameworks to bring back variety, and all of those had to meet the requirement of better than Django in at least some narrow sense, if only in being much lighter, to get any uptake.