Your question touches on a significant and often debated aspect of modern urban design. Many public benches are indeed designed with specific intentions that go beyond simple seating. It's not that comfort is entirely ignored, but rather that other factors are prioritized by planners and architects.
You might notice benches with armrests dividing the seating space. While these can offer support, a primary function is to prevent someone from lying down flat to sleep. Similarly, you may see benches with metal studs or ridges on their ledges and edges. These features are specifically installed to make grinding and sliding difficult, effectively deterring skateboarding.
This design approach, sometimes called "hostile" or "defensive" architecture, stems from complex urban management goals. The intent is often to maintain order, ensure benches are available for their primary purpose of sitting, and discourage activities deemed inappropriate or damaging to public property. It represents a balance—or sometimes a tension—between offering public amenity and enforcing social norms. So, to directly answer your question: yes, many benches are consciously designed to discourage both sleeping and skateboarding, reflecting broader decisions about how public spaces are used and managed.