It's because companies are trying to make a profit, and instead of taking a risk with a series like eva\gits\lain they KNOW they are going to make money making absolute shit like bleach and naruto, dragging it out as long as possible to milk every penny out of it.
BUY shit you really appreciate, even if you have already downloaded it, and make sure you buy it in a manner that you know money is going to make its way back to the creators\producers. That is the only way.
The only piece of anime I ever paid for was a eureka 7 episode that I couldn't find anywhere back when I was a complete newfag. I will be buying the rebuild box set, knk box set, probably something gits and probably elfen lieHARUHIDVDS.