That's how copyright law works. There's no "use it or lose it" provision. Once you create something it is yours, and others only get rights to it 70-100+ years later.
That's only how it works since 1992/1998. Prior to 1992, you had to renew your copyright explicitly after 28 years (for another term of 47 years). 1992 made that renewal automatic. (1998 extended it by 20 years).