Why Overlord did not target Belgium

If Belgium was such a useful position for invading Britain, why did Overlord not target Belgium?

It was heavily defended, and the currents were considered less favorable for an invasion from Britain into Europe.

Belgium's usefulness as a possible base for attacking Britain does not automatically make it a favorable destination for an invasion from Britain. Heavy defenses are one obstacle identified here. The same currents are said to make movement toward Britain more favorable than movement in the opposite direction. German expectations of a British attack in that area add another reason for its defensive strength.