... it doesn't?

One of the downsides of MVTs and the typical max zoom level of 14 is that that they do require more local resources than simply rendering a 256x256 bitmap.

For OSM the question is naturally would a complete migration (aka turning off raster tile support) exclude any noticeable number of people from contributing.

But right now that decision is still a long way off, the vector tile service hasn't even been integrated in osm.org yet.