Because the style doesn't know about that. Penrose is inherently an interactive constraint solver and you need to supply such implicit assumptions for a visually pleasing result. At the first glance I guess `objective centerLabel(...)` will do.

Interesting. Which constraint solver does it use, or do they use their own one?

Hi, Katherine here—we've written our own code for numerical optimization (via L-BFGS) and constraint solving (via the exterior point method).