"Round up the usual suspects"

So France, in an attempt to shut the stable door after the equine had bolted, apparently raided something like 75 assorted houses and compounds, seeking suspects in the terrorist attacks of Friday. Seems they found a "significant amount" of weapons and explosives.

Gotta  Do Something..., I get that.....More importantly, the police and other authorities gotta be SEEN Doing Something.

But here is the question: If they knew where to look, and had reasonable suspicion to execute a search (and were, apparently correct in their suspicions) then WHY DIDN'T THEY DEAL WITH THE ISSUE of the terrorist safe houses BEFORE the attack?  Why did they wait until AFTER some of their countrymen had been killed and injured? If they were raid worthy on Saturday or Monday, WHY WERENT THEY RAID WORTHY ON THE THURSDAY BEFORE THE ATTACKS?

Did their inaction result in increased casualties and deaths?