Courteeners are a massive live band. I didn’t appreciate quite what a fan base they have, but they do. Could headline the Other Stage easily. It won't please the pop lovers or the beard strokers, but there you go.
Having someone like the Spice Girls would be an ironic fun gesture - mid afternoon slot. No chance would they waste a headline slot on it. And crucially, the new dates are all about the money. Debts to pay.