Deleted_by is not changing while i delete a data using observers; - laravel

Question

I want to have fields created_by,updated_by and deleted_by and want to update these fields automatically. created_by,updated_by is working but deleted_by is not working.i am using an observer to perform this task. When i use dd($model) in deleting function in observer it shows the collection or values but the deleted_by is not updating.
My model
namespace App\Model;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletes;
use App\Observers\UserIdFinderObserver;
class supplier extends Model
{
use SoftDeletes;
protected $fillable = [
'name', 'address', 'contact','contact_person_name','country','email'
];
public static function boot()
{
parent::boot();
$class = get_called_class();
$class::observe(new UserIdFinderObserver());
}
}
my migration file
public function up()
{
Schema::create('suppliers', function (Blueprint $table) {
$table->id();
$table->string('name');
$table->string('contact_person_name');
$table->string('country')->nullable();
$table->text('address')->nullable();
$table->string('contact')->nullable();
$table->string('email')->nullable();
$table->string('created_by')->nullable();
$table->string('updated_by')->nullable();
$table->string('deleted_by')->nullable();
$table->softDeletes();
$table->timestamps();
});
}
My delete function in controller
public function destroy(supplier $supplier)
{
try{
$supplier->delete();
return redirect()->route('supplier.index')->with('success', 'Supplier is deleted successfully');
}catch(Exception $e){
return redirect()->back()->withErrors($e->getMessage());
}
}
My Observer
namespace App\Observers;
class UserIdFinderObserver
{
private $userID;
public function __construct(){
$this->userID = auth()->id();
}
public function saving($model)
{
$model->created_by = $this->userID;
}
public function updating($model){
$model->updated_by = $this->userID;
}
public function creating($model)
{
$model->created_by = $this->userID;
}
public function deleting($model)
{
$model->deleted_by = $this->userID;
}
}