It seems that the development of drugs is such an incredibly expensive investment that you need to grant a limited monopoly to the developer so that he can recoup on it.

Average cost to bring a new drug to market is around $1.5 billion

Drug production is (to oversimplify, please correct) to blindly create millions of combinations, test the successful-looking versions on rats, cats and people, and produce billions of the drug. I wonder how the money is split between those tasks.

The biggest expense is typically human clinical trial where you're looking at a figure in the high hundreds of millions.