Why do you think patents are commonly used even though they lead to monopoly problems?

The U.S. Patent and Trademark Office defines a patent as “an intellectual property right granted by the Government of the United States of America to an inventor “to exclude others from making, using, offering for sale, or selling the invention throughout the United States or importing the invention into the United States” for a limited time in exchange for public disclosure of the invention when the patent is granted”. Patents are thus a monopoly right to use an idea and, in the U.S., for utility patents, the most common type, that monopoly right may last for 20 years from date of filing. Suppose a legislator introduced a bill that would decrease patent life for new drugs from 17 years to 10 years, based on the argument that it would reduce deadweight loss through lower prices.
What argument could you make against such a change? Why do you think patents are commonly used even though they lead to monopoly problems?
Must below 150 words