Why does anime never finish the manga storyline?

So, why does a single anime season air or 8 seasons will air... but never finish the rest of the manga storyline?

Bleach is a perfect example. It did a little over half, and than stopped.

Guyver and Claymore are great examples as they only got one season.

Does it have something to do with the ratings?

And what about anime that was super successful that could have finished going all of the way? What about that?

Some manga series finish and are pretty much done, and they still haven't started a finishing series with an anime.

This makes anime a little discouraging to watch as I feel its just a promotional thing for us to head on over to barns and noble to buy the manga series to learn more. As not all of us anime fans like having our heads in a manga book.

Probably because they caught up to the manga, and they could just add filler, or they could stop. Also, the series can really spiral downwards if they are already adding filler. Sometimes some series will stop, and then pick back up again a few years later so then there is more manga content. As for the specific titles you asked about, I don't know too much about those.

And what about anime that was super successful that could have finished going all of the way? What about that?

Perhaps the animation company ran out of money and/or it just wasn't profitable enough for them to keep running the series. Many companies that seem successful on the outside, can really be having financial difficulty that they don't share with the public.

Some manga series finish and are pretty much done, and they still haven't started a finishing series with an anime.

Just because the manga finishes, the animation company really has no obligation to finish the series.

This makes anime a little discouraging to watch as I feel its just a promotional thing for us to head on over to barns and noble to buy the manga series to learn more. As not all of us anime fans like having our heads in a manga book.

Quite a bit of the time it is just promotion. Although, I wouldn't say that it is discouraging, as if it just didn't finish, I'll go onto the next thing in my list. Also, perhaps you need to watch more 1 and 2 cour anime which usually skips manga content, but many times, they do finish the series. Especially if the mangaka is somehow involved in the production of the anime.

Yeah, I agree, it is discouraging. Because many times, if not most of the time, anime adapted from manga are usually just doing exactly that - promoting the source material. They are far more quality than American movie adaptations, of course, but it's still a bit disappointing if you have heard about so-and-so manga title that was written so well that you wanted to check out but don't have any interest in reading.

I'm a bit of purist when it comes to that, as I prefer to know what the original artist had intended to tell. But over the past few years, I guess certain people have persuaded me a little bit to be more open-minded, and I guess some of these adaptations are written pretty well. Just avoid most of those long-running series and stick with drill's advice on 1 and 2 cour anime; they are usually written with the story in mind, not the profit in mind. Then again, some production companies cut down an anime to 1 or 2 cour because of the budget, so don't have any naive illusions about that either.