They fought the Hundred Years’ war to be part of the continent but that was a long time ago
"Calais was regarded for many years as being an integral part of the Kingdom of England,
with its representatives sitting in the English Parliament. The continued English hold
on Calais however depended on expensively maintained fortifications, as the town
lacked any natural defences. Maintaining Calais was a costly business that was
frequently tested by the forces of France and the Duchy of Burgundy, with the
Franco-Burgundian border running nearby. The British historian Geoffrey Elton
once remarked "Calais—expensive and useless—was better lost than kept".
The duration of the English hold over Calais was, to a large extent, the result of the
feud between Burgundy and France, under which both sides coveted the town, but
preferred to see it in the hands of the English rather than their domestic rivals."