I have worked in the Royal Palace in Stockholm over the years, and also visited as a tourist. I love looking at the furnishings and architecture. There are things you never see in your normal life, in terms of master craftsmanship and expertise. Royal Palace staffing requirements hundreds of years ago were like whole villages of people who could do all kinds of things – metal workers, leather tanners, textile workers, artists, sculptors, master masons, seamstresses, furniture makers, etc etc. These artisans lived and worked within the palace walls, producing things that the man in the street would never experience. Just the grand scale of everything and the stunning ceiling murals are enough to stun you into silence.
Many of this artisanal knowledge does not exist today, even though the proof of its existence is still out there in palaces and museums all over the world. The Stockholm Palace has expert restorers working constantly to keep existing examples of old craftsmanship alive. There are, however, certain textiles that cannot be restored because no one knows how to perform that specialised skill anymore. Some of the masonry is done using methods that are no longer passed down from one generation to another.
There is another issue as well in that in the times these huge edifices were built and their contents were produced, cost was of no consequence. Monarchs often spent to excess to show their power and wealth, and functionality was often not a priority. Neither was the safety of workers. Nowadays cost-cutting is key, particularly if it is state-funded. And methods must support a safe work environment.
This is probably going to be an issue with the restoration of the Notre Dame. Built in the 12th and 13th centuries, attitudes were much different when it was built. Not to mention that there is probably not enough forest nearby to rebuild the entire roof. Will there be expertise and knowledge enough to recreate what was lost? Will the cost of it become a huge issue, given that many will feel there are more deserving causes which need the money more?