Actually, it does.
It checks in the background for what size the document is. If it’s an aspect ratio that matches up to 12x20 (3x5 aspect ratio), it knows how to scale a file if the file is unitless, or defined in pixels.
Why? Because different programs use different default interpretations of pixels per inch. If you make a 1” square in Illustrator that in the SVG code is defined as 72 pixels (what Illustrator uses - 72 PPI), when you bring it into the app, it will be a different size since most browsers use 96 PPI.