It’s not weird. When you’re dealing with an organization as big as the US government, you’re not going to be able to standardize on a single technology for front end engineering. So you say “Make all your stuff look like this” as an opening statement, and then secondarily work with certain large departments to implement the visual stuff (1em padding on modals, 5px rounded edges on cards, tooltips on icon buttons etc) in the technology that each is using.

You won’t be able to get to everyone, but the people you don’t get to (say, the DEA weirdos using MooTools and Stylus) will at least have some guidelines they can follow instead of just coming up with styles on their own.