Because there is a French law prohibiting this. It wasn't just bad taste, it was against the law.
“Because there is a French law prohibiting it”
There are laws prohibiting many things Frenchmen do, but not a national manhunt to track down every perpetrator. If you can’t see they’re getting special attention for being royals, you’re blind. And if they don’t see it’s in vain since the bell can’t be unrung, they’re plain dumb.
It could also be that the French are a little sensitive given what happened to Diana.