By default, Search Filters work with an exclusive behavior.
It means that if you select two filters, the store locator will only show results that have BOTH filters assigned. This is called an 'AND' behavior.
If you want to change it and use an inclusive behavior, you can update your Search Filters Behavior from this page.
Exclusive Behavior
If you select Filter A and Filter B, you will see results that have Filter A AND Filter B assigned.
Inclusive Behavior
If you select Filter A and Filter B, you will see results that have Filter A OR Filter B assigned.