1. Ah, I remember the 70s, and its architecture. In fact, I remember it so well that I remember when it was all brand new and pretty and used extensively in various science fiction TV shows and movies as What The Future Will Look Like.
Which aesthetic, like pretty much everything else from the 70s, has been soundly rejected. Alas, you can easily toss that polyester leisure suit and replace that avocado green tile in your kitchen. You can't quite as easily toss that three-city-block government office you built back then.
2. Concrete is a pretty awful material to work with. In retrospect. It does not at all age well. And, let's face it, Washington, DC, sits on a swamp. Lots of humidity and heat and rain and all that will make any building look a bit worn, and concrete most of all.
(Visit London some time, if you don't believe me.)
Add to that what I strongly suspect is seriously tight capital maintenance funding for government buildings (because why should they be treated any differently from the rest of our infrastructure?), and it's not at all surprising that these structures (and their surrounding grounds) are not aging well.
Sure, they're going to keep the buildings on the Mall and other tourist locales in shape, but if we're letting our major bridges and interstate highways fall apart, what are the odds we're going to keep the Dept. of Housing and Urban Development headquarters looking shiny and pristine. Especially when there are plenty of folk in DC who'd just as soon see it abolished.
The 7 Ugliest Government Buildings In Washington, D.C.
DO NOT PROCEED if you are allergic to concrete.