Time is the main thing. Nowadays, if you want a building, you go with the architects and builders who can give it you quickest (and cheapest). But the Pharoahs, kings and priests back in the day were happy to wait years, even decades. for the work to be done properly. Which is why the Pyramids will still be standing when the Shard is rubble. We are in too much of a hurry today!

There is also craftsmanship. An item made from scratch by someone who has trained and studied for a lifetime will always be superior to one assembled in a factory by people who don't really understand what they're making.