[Nyx]

That's right, is not that hard, sometimes i think those people in charge don't even know that the manga exists.

Let's take Rosario Vampire for a prime example [SPOILERS AHEAD]

They completely changed it. For the first 'season' the followed along great with the original manga series, but when it came time to make Capu 2 to follow along with the continuation of the manga, it turned more into avoiding the other girls and trying to fuck Moka. In the manga it's about trying to survive when a terrorist organization comes after the group and Tsukne is learning to cope with his new powers as a half vampire. The anime twisted that into Tsukne is trying to get permission from Moka's father to date her, goes to his castle and fights him using a headbutt fucking thing and wins the day. The manga turned out to be amazing but the anime is still getting scores of like 4/10 to this day. I seriously hope the writers for the anime realized how much money they missed out on if they weren't complete fuck ups.