Probably because satellites in LEO are too low to get such a broad view, and the camera-equipped satellites that are higher up are all over the equator.

http://nsidc.org/soac is a pretty good resource.

https://www.nesdis.noaa.gov/content/imagery-and-data has a nice display of actual images.

Is it? Landsat is polar, so it should be there. Is this just a projection issue?