Netflix isn't maliciously saying all of their shows can only run for 3 seasons and then have to be cancelled. It's just what they are doing to shows that are below their expectations/getting middling viewership (in their eyes). They have shows that have gone on longer, in some cases much longer -- clearly the ones that do the best for them. Stuff like OITNB, House of Cards, Narcos, Grace and Frankie, Fuller House, Bojack Horseman, etc.
At the same time, Netflix produces a ridiculous amount of original content (some would say an unsustainable amount), and that just naturally results in it being much easier to ditch a program when there's so many others that could potentially perform better (or may even simultaneously be out-performing that specific show).
At the end of the day, a 3 season run isn't even bad. Keep in mind that most shows never even get to the point of being made, and even then never even make it past their first season.