Why can’t I overload constructors in PHP?

You can’t overload ANY method in PHP. If you want to be able to instantiate a PHP object while passing several different combinations of parameters, use the factory pattern with a private constructor.

For example:

public MyClass {
    private function __construct() {
    ...
    }

    public static function makeNewWithParameterA($paramA) {
        $obj = new MyClass(); 
        // other initialization
        return $obj;
    }

    public static function makeNewWithParametersBandC($paramB, $paramC) {
        $obj = new MyClass(); 
        // other initialization
        return $obj;
    }
}

$myObject = MyClass::makeNewWithParameterA("foo");
$anotherObject = MyClass::makeNewWithParametersBandC("bar", 3);