Ah, right. “Create Topic” goes away on /categories because “Create Category” needs that space when an admin user is viewing it. I was judging this as a normal user, on meta.discourse.org, without looking at my own instance.
While it contextually makes sense to do that (you’re an admin, on /categories, and you want to make a category, not a topic), it’s actually a fairly bad UX move. Admin or developer chauvinism, really. Besides, category creation is such a rare event that it’s not even convenient. You have to remember that it’s possible, and go there. If I’m looking for that ability as an admin, I’m going to click “Admin” first.