The worker at the counter can become the face of a decision they were never allowed to influence.

The person delivering the decision usually did not make it. They will absorb the anger for a policy they may privately think is wrong, set by people the public will never meet. That arrangement is convenient for the institution, because the frustration lands where it cannot change anything and dissipates before it reaches the level that could.

When you are angry at a counter, it is worth asking who set the rule and how to reach them, calmly, rather than spending it on the person in front of you. If you work in that role, saying plainly that you did not set this and here is who did is honest and often helpful. Directing frustration accurately is the only way it ever accomplishes anything.