Casting datetime does not set timezone to UTC

Couldn't find an answer in the myriad of threads on timezones so thought I might ask.

When setting a datetime casted attribute ('date' => 'datetime' in model) from a Carbon instance in another timezone, the timestamp stored is not adjusted to UTC. My config('app.timezone') and postgresql database timezones are both UTC.

    $date = now('America/Monterrey');
    $statistic = Statistic::factory()->create();
    $statistic->update(['date' => $date]);
    dump([
       $date->toString(),  // => "Wed Mar 06 2024 14:55:34 GMT-0600"
        $statistic->date->toString(),  // => "Wed Mar 06 2024 14:55:34 GMT+0000"
        $statistic->date->timezone->getName(),  // => UTC
    ]);

I would have expected $statistic->date to keep the timezone or be 20:55:34 not 14:55:34 because of the -6 hour difference.

My first question is, should it be automatically converted or that something I must handle? To make it work as I expect I must manually set it to UTC before saving: $date->clone()->utc()

If the answer is that Laravel should handle it, what else could be going wrong on my side? Should I be constructing the Carbon instance differently?

PS. This even happens without updating and just setting values $statistic->date = $date;, and with other attribute names that aren't as confusing as date.

Update: I found this thread where it seems like it is not a default behavior, what a bummer. https://github.com/laravel/framework/issues/19737

In this other thread back n 2013, Taylor said I don't think we should magically convert times to a given timezone but the v10 documentation says By default, the date and datetime casts will serialize dates to a UTC ISO-8601 date string (YYYY-MM-DDTHH:MM:SS.uuuuuuZ), regardless of the timezone specified in your application's timezone configuration option.