There is a large number of TV shows and movies that is not available on any streaming service. There is also a large number that's available, but only from a very specific content provider. For example last I checked, Seinfeld was only available on I think TBS's website, with an awful Flash-based player and really intrusive commercials. Oh, and what was available was something like a set of 5 rotating episodes, not the whole thing. Another example is Conan the Destroyer (been on an Arnold kick lately) which as far as I saw could only be purchased on BluRay or DVD.

I am not saying the content providers owe anyone a streaming option. But grandparent is right about path of least resistance.