The price of joining can be hidden inside transport, clothing, and the hours required.

A free activity is rarely free. Getting there costs a bus fare twice over, the right shoes cost forty pounds, the Saturday morning costs a shift somebody needed, and the kit everybody else already owns costs the price of not looking out of place. The headline says open to all, and the actual entry fee is assembled from things nobody thought to list.

If you run something, write down every cost a newcomer would face and find a way to cover or remove the awkward ones. Spare kit, a lift, a later start. Ask somebody who stopped coming what the real obstacle was, because they will know precisely.