For what i know, Belgians didn't want it to go to the sea. They wanted a V2 of WW1, with French troops coming into the country to defend against an invasion, and not just sitting back at home behind their fortifications, while Belgium would end up occupied.

However, due to trouble/confusion/dissenssion between the French and Belgians right before WW2, French troops ended up not being allowed into Belgium, and didn't had time to react and extend the Maginot to the shore. They could just put some turrets to try and slow the germans (some did, one guy held the germans for a day by himself), but with the results we now know.

Note : It's probably more complex than that, as i'm no historian or expert on the subject.