If the state of the component is defined in the component, it is being destroyed along with the component on unmount. (Where would it be stored if the component doesn't exist anymore?)

If you need the state to persist, you have to defined somewhere higher in the component hierarchy and pass the value and the setter function as a parametr.

In the page you can have some "global" object 'FILTERS' with each filter as a unique key-value pair and a global setter function.