That's not what that chart shows. The satellites are not evenly spaced over the globe. Most of the satellites are in 53 degree inclination orbits: those orbits have zero coverage at greater than 53 degrees latitude, and they have non-uniform coverage of smaller latitudes. (To see this, consider a constellation of 90 degree inclination polar orbits: the poles clearly have a higher density of satellites than the equator. Similar is true for lower-inclination orbits, albeit to a less extreme degree.)