Why my vtk does not contain time series?

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I create my data through apply_inverse(), from mne python, I want to write my data into a vtk file with a time series, however I can only get a static vtk file, don’t know where does wrong. Thanks for your help!
Here is my code:

stc_suf = apply_inverse(evoked, inv, lambda2, inv_method)
    data=stc_suf.data
    # Assuming you have already generated your data and visualized it
    # using stc_suf.plot() and mlab.show()

    # Define the output filename
    filename = 'output_lh.vtk'
    filename2 = 'output_rh.vtk'
    polydata = vtk.vtkPolyData()
    points = vtk.vtkPoints()
    
    # Get the vertices and faces from the stc_suf object
    vertices1, faces1 = read_surface('./test/surf/lh.pial')
    vertices2, faces2 = read_surface('./test/surf/rh.pial')
    for vertex in vertices1:
        points.InsertNextPoint(vertex)
        polydata.SetPoints(points)
    triangles = vtk.vtkCellArray()
    for face in faces1:
        triangle = vtk.vtkTriangle()
        triangle.GetPointIds().SetId(0, face[0])
        triangle.GetPointIds().SetId(1, face[1])
        triangle.GetPointIds().SetId(2, face[2])
        triangles.InsertNextCell(triangle)
        polydata.SetPolys(triangles)

    scalars = vtk.vtkFloatArray()
    scalars.SetNumberOfComponents(data.shape[1])
    scalars.SetName('TimeSeriesData')
    for i in range(data.shape[1]):
        for j in range(data.shape[0]):
            scalars.InsertNextValue(data[j, i])
            polydata.GetPointData().SetScalars(scalars)

    writer = vtk.vtkPolyDataWriter()
    writer.SetFileName(filename)
    writer.SetFileTypeToASCII()
    writer.SetInputData(polydata)
    writer.Write()