But why did it take so long?
Look at it this way, If I were to ask you to produce for me a very simple "dinner fork" made of metal. But today's technology didn't exist. How long would it take you to first comprehend (design) it ie: probably not very long, Then find the metal to make it with, then actually "mine" the metal. Then how long will it take you to find a way to produce a fire hot enough to melt it down into useable ingots ie:roughly 2,000 degrees should suffice. Then you would need to design and build a machine of some sort to actually manufacture it. But then you need a way to power your machine preferably not by chaining a horse or donkey up to it. How long would it take you to acomplish such a feat ?, my guess is that one entire lifetime wouldn't be enough.