People like to say this, but, no offense, it just doesn't seem true. It sounds like a justification. (And I'm not judging, I'm just not convinced by this reasoning).
Signing up for 3-4 streaming services is pretty easy. If you use something like an apple tv or fire tv you can even use a global search that links you into the app where the content you searched for lives. If you're willing to pay per episode or movie to rent or buy everything you watch on itunes or amazon, it's even easier and you can get almost anything instantly.
I do agree that in general, the more different streaming services are released the more that people's incentives are starting to tip back towards pirating. But I don't think there's much other reason beyond just cost.