Very generally, there's nothing wrong with minimizing the bittering hop quantity by using high AA hops. However, the long answer may be fairly complex.
Consider the same question in the context of malt: "why not chocolate malt for color and roasted flavor all the time?" While it's certainly possible to achieve a wide variety of color and flavor solely with 2-row and chocolate malt, you'd be missing out on a lot of flavor, color, and body components available through other grains.
To a lesser degree, the same is true with (bittering) hops. The most obvious example that comes to mind is to compare two hypothetical IPA recipes that are identical in volume, grain bill, mash schedule, boil length, and IBUs. One recipe would use a single high AA bittering addition at 60 minutes followed by a hefty dose of flavoring hops at flameout. The other recipe holds off on the hops until the final 20 minutes of the boil, loading them into the kettle in fairly large quantities in an almost constant stream from 20 minutes until flameout to achieve both flavor and bittering components. Beer #1 (with the high AA addition) will likely have a more assertive bitterness with a lot of grassy flavors, while Beer #2 will have a smoother bitter character and a ton of hop flavor complexity. While this is an extreme example, it should be fairly clear that the high AA bittering technique, while excellent in times of hop crisis, is not necessarily the panacea of hop bittering techniques.