Somehow, it got into everyone's brain that making more expensive, shorter games with less that zero replay value was the way to go. The catchphrase of the day was (is) "cinematic gaming" in an ever enduring quest for games to be taken seriously as an art form by... umm... mimicking another art form.
Let's have a little self-awareness party here shall we? Gaming, has been, and always will be entirely gimmick-based. Game developers are as prone to faddism as their clientele and will nearly always hop on the next "Me-Too" bus because the consumer base is largely consistent of attention-deficient "impress-me-now's" that unless you have bump-mapping, force-feedback-ing, moral-choice-metering, downloadable-content-ing, online-multiplayer-ing goodness in your title, consider you yesterday's news. We're a bunch of gameplay mechanic fashionistas that demand the newest available technology be injected into everything we open our wallet for... which is how you get fantastic games like Duke Nukem Forever.
The reason why the second dimension is one of the most important Princesses to save in my mind is much akin to the reason a haiku exists: Creativity bred from limitations. When you have to make a compelling experience in a technically limited space, the creative mind taps into a different part of the right side of the brain and forces the creator to be a different kind of creative than they would be with seemingly limitless possibilities. Imagine if you had to create a game like God of War in only two dimensions. Immediately your brain starts tapping into a different type of thinking; the kind that makes us figure out ways to fit square pegs into round holes. This is what made the SNES/Genesis days give us some of the most memorable experiences in gaming to this day, and why some of the best games on the first-gen 3D consoles were still brilliantly rendered in two dimensions (read: Castlevania: Symphony of the Night).