Does anime that isn't from a manga or light novel cost more to make than adapted anime? If so, why do they make original anime if studios only want anime that makes money?
If anything, anime adapted from a manga, light novel, or visual novel should cost more to make because there would be costs associated with working with the owners of the original. But make no mistake, studios do only want to release anime that make money.
Why are so many anime based on existing properties?
The focus on anime based on existing properties is not about production cost; it's about risk management.
Whenever you're selling creative work to a mass market, you're taking a huge risk that it won't catch on and you won't make back what you spent on it. If you're selling cola or toilet paper or office furniture, it's relatively easy to do some research, figure out what consumers want, and make that. It's well understood what consumers want out of these products, and you can distill your consumers into a small number of profiles that you can serve by a line with two or three varieties of your product.
But this is much harder when it comes to creative work. You can get together a focus group and give them surveys on what they like about Naruto, One Piece, and Dragon Ball Z, and then try to make an anime series based on that knowledge, but it will fail. Audiences can tell when you're making a creative work based on market research, and they will hate you for it. Well, to be fair, this isn't always true. You can sometimes get away with cloning an existing series, especially with properties aimed at children. It always boggled my mind that Beyblade became so popular when it was such a transparent knock-off of Pokemon, Digimon, Yu-gi-oh, and Monster Rancher. But you can only get away with this for so long; children will grow up, and even the least discerning audience will notice after your third clone of Naruto that you're just repeating yourself. Audiences want certain comfortable tropes to stay in place, but they also want a certain amount of novelty. And no focus group will ever lead you to true originality.
But originality is risky; there's always the chance that audiences won't respond, and your sales will suffer. As one example, consider the two concurrent yonkoma manga of Satoko Kiyuzuki, Shoulder-a-Coffin Kuro and GA Geijutsuka Art Design Class. Both are seinen yonkoma series that started in 2004, which means they were expected to be schoolgirl moe slice of life cuteness. GA is; it's a conventional moe yonkoma about five high school girls having fun at art school. Kuro is not; it's a dark fairy tale with only the lightest of moe elements. Guess which of these two got an anime adaptation?
However, if Kuro had turned out to be a massive breakout success, I'm sure it would have gotten an anime adaptation, because that's why so many anime are based on existing properties: the anime studios let sales of the original work tell them what kind of potential an anime based on the property has, and if the numbers tell the right story, they'll pull the trigger on an adaptation. This is why there are anime based on Oreimo, Oregairu, and One Piece, but none based on The Circumstances Leading to Waltraute's Marriage, The Zashiki-Warashi of Intellectual Village, Guru Guru Pon-chan, or Enmusu (despite the first two being written by A Certain Adjective Noun series author Kazuma Kamachi).
Why are original anime still made if they're so risky?
A lot of us older fans like to focus on the business side of anime, because younger fans tend not to understand how much the business side influences the creative side. They tend to think that anime is always made with the creative impulse at heart and the creative people are in charge, and thus struggle to understand why certain artistic failures happen. I definitely thought this way when I was a younger fan.
But while there is a cutthroat business side to anime, and there is a lot of cynical, money grubbing behavior in the industry, the creators do still have some control, and sometimes, after they go out and rake in the cash for the studio with stuff based on existing properties, they want to exercise their creative muscles a little. Take Cowboy Bebop: if you believe director Shinichiro Watanabe, he was pretty much given free rein to do whatever he wanted with it after the toy companies pulled out, and he made something experimental and original which wasn't a massive financial success, but is beloved by fans. Bandai Visual trusted Watanabe to deliver based on the strength of his premise and his previous successes with Macross Plus and Mobile Suit Gundam 0083: Stardust Memory. Madoka? Similar story: director Akiyuki Shinbo, who had just recently finished reaffirming his value to Shaft with Hidamari Sketch and Bakemonogatari, pitched his plan for a new magical girl series to producer Atsuhiro Iwakami, who trusted Shinbo enough that he consciously decided to let Shinbo build his own original work instead of tethering it to an existing property. Iwakami himself says that after helping assemble the team of Shinbo, writer Gen Urobuchi, and character designer Ume Aoki, he purposely stood back and let the creative people work:
ANN: At the Q&A you also mentioned that you had asked Urobuchi specifically to write something "heavy." How much guidance do you offer on the creation process?
AI [Iwakami]: I was the one who said "let's do a show using these creative talents." But after that I don't matter much; it's up to those talents to do their work. If something comes to a stand-still I might intervene, but they did an excellent job and I was very happy seeing the results in episode one. When I saw the character designs that Aoki did, it was exactly what I was hoping for, so everything was in the hands of the creative team.
From Anime News Network
Original anime are riskier to make because there's always a chance they won't catch on with audiences and the studio won't make its money back. But they can also pay off in a huge way. If every single anime that comes out is based on an existing story, there are people who will stop watching anime altogether; they'll either read the original work instead, or they'll move on to an entirely different medium where originality is more prized.