Why are Delphi objects assigned even after calling .Free?

program Project1;
{$APPTYPE CONSOLE}
uses SysUtils, Classes;

var
  sl : TStringList;

begin
  sl := TStringList.Create;
  sl.Free;
  if Assigned(sl) then
    WriteLn('sl is still assigned')
  else
    WriteLn('sl is not assigned');
end.

procedure FreeAndNil(var Obj);
var
  P: TObject;
begin
  P := TObject(Obj);
  TObject(Obj) := nil;  // clear the reference before destroying the object
  P.Free;
end;

procedure TObject.Free;
asm
        TEST    EAX,EAX
        JE      @@exit
        MOV     ECX,[EAX]
        MOV     DL,1
        CALL    dword ptr [ECX].vmtDestroy
@@exit:
end;

var
  sl1, sl2: TStringList;
begin
  sl1 := TStringList.Create;
  sl2 := sl1;
  FreeAndNil(sl1);
  // sl2 is still assigned and must be cleared separately (not with FreeAndNil because it points to the already freed object.)
end;




procedure TObject.Free;
asm
    TEST    EAX,EAX
    JE      @@exit              // Jump to exit if pointer is nil.
    MOV     ECX,[EAX]
    MOV     DL,1
    CALL    dword ptr [ECX].vmtDestroy  // Call cleanup code (and destructor).
@@exit:
end;

if Obj != NIL then
  vmtDestroy(obj);  // which is basically the destructor/deallocator.