There are two kinds of anime, and they're very similar to the two kinds of personal computers we have today. Studio Ghibli produces the kind of anime that's identifiable to Apple products—it's high-quality, expensive, has its own style, and is aimed at a very wide audience, sometimes ending up in American theaters. Additionally, the content (software) produced to go along with the format (hardware) is developed in-house.

Meanwhile, most other anime producers are like PC manufacturers—they compete to produce a commodity as cheaply as possible. First, they're adapting manga that has already been written, illustrated, published, marketed, and merchandised, so the customer development half of their business doesn't need doing. They simply churn out adaptations of the books they receive, and people tune in; it's a pre-made market.

Second, people don't care about the visual quality of anime. It's great when it's exceptional (I can only think of Ghibli work and FLCL at the moment), but no one expects it to be. Mostly, anime-watchers tune in to experience a visual dramatization of a story that couldn't be executed in live-action without a ridiculous budget. Things in space, giant robots, fantasy creatures that aren't just actors with bumpy foreheads, etc. They don't expect great visuals, just the bare minimum needed to understand what's going on, so they can enjoy the story without having to imagine the narrative themselves (and though they do still end up having to read the dialogue, this doesn't require any form of visual imagination.)

Given these two factors—that the studio's only job is to adapt a manga to the screen, and that they may do this as badly as possible and still not lose any of their following—it's no surprise that it's a process that has been outsourced and reduced to manufacturing "more work with longer hours = better" conditions.