The short answer is: because if you don’t renew it, you will lose your patent.
The Purpose of Patent Renewals
There are two reasons a patent office requires every patent holder to pay a regular renewal fee. Firstly, it generates income for the patent office that allow it to continue its work of providing the intellectual property protection system.
Secondly, the purpose of the patent system is to promote innovation and economic growth. Patent owners who make a commercial success of their product or service can protect themselves from competition for a limited period of time by enforcing their patent rights. If they are unable to commercialise their invention, the imposition of fees encourages patent owners to relinquish their rights to make them available for general use by other parties to use and develop.To find out more about the basics of patent renewals, read the Introductory Guide to Patent Renewals.