Calling php artisan db:seed does not work without providing a class name

I have a seeder class in the database folder

class UsersTableSeeder extends Seeder
{
    public function run()
    {
        $user = new User();
        $user->name         = 'Name';
        $user->email        = 'email@gmail.com';
        $user->password        = bcrypt('secret');
        $user->save();

    }
}

When I run php artisan db:seed nothing happens, the seeder is only called when I run php artisan db:seed --class=UsersTableSeeder

This means I have to call each seeder class separately, any idea why db:seed doesn't work by it self?

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