Good question—I’ve noticed this too, and it usually comes down to practical street-level design rather than looks. A domed top acts like a little roof. Rain runs off instead of pooling on a flat lid, so the waste inside stays drier. That matters because wet trash smells worse, gets heavier, and turns into a messy slurry that’s harder for crews to empty. A dome also keeps rainwater from flowing through openings and leaching out around the base.
There’s a pest angle, too. Flat tops can collect rainwater, food residue, or a discarded cup, which attracts flies, wasps, birds, and rodents. Domed lids reduce standing water and make it harder for people to leave drinks or wrappers on top. Many domed bins also have side or hooded openings that let people toss trash in while shielding it from rain and wind.
Structurally, a curved top can be stronger than a flat panel, and it doesn’t create a ledge where litter accumulates or people sit. Some cities also choose domes to discourage scavenging and to make urban waste bins easier to clean. It’s a small piece of street furniture design that solves several problems at once. That said, not every urban trash can is domed—flat-top bins may be used where accessibility, signage, or specific collection systems matter more. But in busy streets with rain and pests, a domed top is a simple way to keep the bin cleaner, drier, and less smelly.