I’m not claiming the French people don’t care about Notre Dame. I’m merely observing that the analogy to the Declaration of Independence is significantly flawed. Notre Dame embodied ideas that modern France has repudiated rather than upheld.
History and culture are very important to the French people. Our Lady of Paris is one of the cores of the city.
The country and government being secular does not mean that the people left their Catholic roots behind. Atheist and religious French people share similar values and the past is very important to both.