As with Tesla and other brands making EVs from scratch, the MEB platform is designed explicitly with electric power in mind. The floorpan is designed to house a flat, high-capacity battery that simultaneously improves handling (by lowering the center of gravity) and space. VW also promises comparatively fast charging on every I.D. car -- you should reach 80 percent capacity in half an hour.
While that initial wave is bound to spread across multiple years, the 10 million figure is a reminder that VW sees MEB as the key to taking electric cars mainstream. For context, the Auto Group sold 10.7 million vehicles worldwide in 2017. EVs may still represent a minority of VW's sales, but they'd be far more commonplace than the niche models you see from the company today.