KML files contain geographic information (usually points and polygons described by sets of latitude and longitude coordinates) in a specific projection. That makes it easy to overlay the geometries described in a KML file on a map, for example with openstreetmap of google maps. And it makes it possible to display information on it that also has latitude and longitude attributes.
SVG files contain definitions of shapes like triangles, squares or polygons. An SVG file can be shown on it's own, but it can't be shown on a map. There's no information about where these shapes exist in the real world. To be useful the shapes need to have an identifier, for example a region name or a room name on a floor plan. This identifier can be linked to other data (a count or sum of something) to create for example heatmaps.
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