When will Netflix add more episodes?

I just finished watching 90210 but there is only 3 seasons on netflix but when I watched it on tv there were 5 all together. It finished over a year ago so why Netflix does not have all of the seasons by now? The same goes for Adventure time ( there's only 1 season on there) Why don't they have American horror story? Or other series? I'm paying money for nothing in a way and it's really irritating So does anyone know when Netflix will add all of the episodes ?