It's a UI around the Mapnik raster map rendering engine and the CartoCSS styling language. The idea is that you write your stylesheets and see the map's appearance change accordingly. It was originally developed by Mapbox, but they've since moved to vector rendering.
Yes, but it's still grounded in technical terms. What kind of end user use cases are supported by this tool?
Does this help me create an overlay layer for Google Maps? Does this help me embed a map widget on my own website? Does this help me remix open-source mapping data to produce a customized rendering? Does this help me create maps for my fantasy RPG campaign setting?
Yes, I can do some googling and research these terms and figure it out, that's not the point. The point is that this website does not do a good job of telling a random person (or random developer) why they might be interested in this tool and what it can do for them if they are not already familiar with web map viewer technology..
Not every website is intended for a random person (or random developer), especially in the open-source space, and especially when the developers don't want to take on the support burden of users who do not have a certain degree of background knowledge.
(Not disagreeing with your point.)