I dunno, maybe so they're not breaking the law? You know, strange as it might sound, some people think that stealing is wrong. And I dare you, walk into a store, grab a TV, and walk out with it saying that you'll pay for it later. See how far you get.
That's not the same thing. If I took the TV then the store loses out because it is not able to sell that TV any longer, chances are I'd also get arrested. Watching the sub online poses no risk to me and Toei isn't going to lose out on it.
Piracy does have it's advantages. I watched the entirety of DB/Z/GT and the movies as well as reading all the manga for the first time on the internet without paying anything, I became a fan of it which led to me later buying the entire show on DVD and all the manga as well as other things. This is not something I would have done if I hadn't watched it "illegally" in the first place because I'd have never have bought it out of curiosity.
Naruto and One Piece I've also spent hundreds of pounds on that I never would have if I hadn't watched it online first for free.
There are shows that I like that were never released outside of Japan and were never officially subbed into English so that leaves me two choices either never watch the show at all or just watch a fansub. In this case watching the fansub is no loss to the companies because I'd have never have bought the DVD anyway if it's not in my language.