Terror in Belgium: wild goose chases, chemicals for making cheese

The main surviving perpetrator of the Paris terror attacks, Salah Abdelslam, is now on his way to Germany after the Belgian security forces, intelligence and military failed to capture him in Brussels, the Belgian authorities said at the beginning of the third day of their lockdown on the capital. It can be assumed that we will hear within a few days that the majority or all of the 16 people arrested during the Belgian military's large "operation" in Brussels will be released soon.
Prime Minister Charles Michel said "I indicated yesterday that what we are concerned about is an attack similar to the one that was carried out in Paris involving several individuals and maybe targeting attacks on several sites simultaneously." In other words, he has no information on the people involved or where the attack will take place.
If that is the case, why is it necessary to close the capital city with close to a quarter million residents, including all of its transportation systems, educational institutions, coffee shops, restaurants and bars?
In order to justify the step, the Belgian government issued a warning that the city faces the threat of a chemical or biological attack, which   headlines and sparked fear worldwide. However, there was no information or sign of such a threat from any of the searches or arrests carried out by the Belgian authorities, except for some chemicals that were later found to be intended for making cheese. There was no sign of such a possible attack in Paris either.
Brussels is a small city that hosts the headquarters of NATO, the largest Western military alliance in the world, as well as those of the European Union and the European common market. They have suddenly become silent, as if international terror is not their concern.