Because when on a new tab, tapping blows up top sites icon size and removes second line of text, it becomes very difficult to identify sites (e.g. I have many YouTube channels as top sites; they all have the YouTube icon, so you need to see the text to distinguish them).
The view is perfectly OK (smallish icons, two lines of text) UNTIL you tap when icons blow up is size and text reduces to one line and only 4 or 5 characters.