为什么子类不能覆盖父类的“__debugInfo”？

问：

这是我的代码：

use Carbon\Carbon;

class Demo extends Carbon
{
    public function __debugInfo(): array
    {
        return ['value' => $this->__toString()];
    }
}

$d = new Demo();
print_r($d);

我所期望的输出是这样的：

Demo Object
(
    [value] => 2023-05-23 13:57:18
)

但我得到的是：

Demo Object
(
    [endOfTime:protected] =>
    [startOfTime:protected] =>
    [constructedObjectId:protected] => 00000000000000020000000000000000
    [localMonthsOverflow:protected] =>
    [localYearsOverflow:protected] =>
    [localStrictModeEnabled:protected] =>
    [localHumanDiffOptions:protected] =>
    [localToStringFormat:protected] =>
    [localSerializer:protected] =>
    [localMacros:protected] =>
    [localGenericMacros:protected] =>
    [localFormatFunction:protected] =>
    [localTranslator:protected] =>
    [dumpProperties:protected] => Array
        (
            [0] => date
            [1] => timezone_type
            [2] => timezone
        )

    [dumpLocale:protected] =>
    [dumpDateProperties:protected] =>
    [date] => 2023-05-23 13:57:18.314578
    [timezone_type] => 3
    [timezone] => UTC
)

有什么想法吗？