Bus Éireann ticket prices don’t add up

Can someone explain to me the logic of Bus Éireann ticket prices?

Because my journey from Limerick to Skibbereen, last weekend, was broken in Cork, a ticket which should have cost €40 return (Limerick to Skibbereen), was subject to a €12 surcharge.

This consisted of a €22 ticket — return from Limerick to Cork — and a €30 ticket — return from Cork to Skibbereen.