Why does the salt bridge in the galvanic/voltaic cell maintain the potential difference instead of neutralising it?

The potential difference between the copper and zinc plate pulls the electrons in the wire but not the ions in the salt bridge. Why this discrepancy ??

Suppose there was no salt bridge.. then the electrons upon reaching its destination would have reduced the potential difference to 0 by producing an opposing electric field that cancels the existing one. But the ions in the salt bridge prevent this by flowing opposite to the electrons maintaining the potential difference as constant.

But why do the ions behave differently from the electrons? Why don’t they all move in the same direction towards copper and reduce the potential difference ? Why does the salt bridge chooses to save ?