Are they rare? Aren’t credit unions worker cooperatives? Insurance is often structured this way, and I’ve heard of farmer collectives too. I have a worker cooperative grocery store nearby. I do photography as a hobby and there’s all kinds of photography cooperatives, including Magnum which is incredibly famous in that world. I’m in an HOA which is another cooperative.
Most "co-ops" are customer co-ops (Credit Unions, for example, are owned by their members, most grocery co-ops are membership programs, REI is/was the same). Farmer co-ops are owned by a collection of farmers, to pool resources for selling to consumers, but most employees aren't co-owners. Worker's co-ops are rarer, but you find them in the taxi industry pretty often, and in home care.