Accessibility. If CSS is disabled, it will render the data table.
The way this library works is the data is embedded in a table, which then gets converted to a chart by CSS - so if the CSS is disabled, the data is just presented as a table of numbers.
I'm not sure if SVG can be written so that it gracefully falls back like that. You could generate SVG from the table using JavaScript, of course, and just hide the table with JavaScript.
2. I want a graph, not a table. SVG is self-contained so WYSIWYG, always.
3. If you want to show both a graph and a table, with Charts.css your markup would contain the same table twice.