Trademarks don’t have to be original at all. The name Captain Marvel certainly wasn’t original when Marvel Comics trademarked it. They just took advantage of the fact that DC had allowed the trademark to expire.
As @Otherbrother pointed out above, the purpose of a trademark is actually to protect consumers as much as it is to protect the rights of the IP holder. Without trademarks, anyone could produce a sneaker with a swoosh on it and make consumers think it was a genuine Nike. Well…that does happen now, anyway, but it is illegal and there are recourses for going after companies who do that, because of trademark law. This is also why you can have two businesses with virtually the same name, both trademarked, as long as they are in completely different industries/markets. There’s no chance of brand confusion.
Copyright, on the other hand, exists solely to protect the copyright holder, who often isn’t the creator, sadly. And yes, it is waaaaay too long.
