问tkinter 为什么控件无法放在Frame中？

import tkinter as tk
from tkinter import filedialog

from PIL import Image, ImageTk

class MY_GUI():
    '''
        人脸识别系统UI界面
    '''
    def __init__(self, app_window):
        self.app_window = app_window
        self.file_path = tk.StringVar(value='./image/test_sample.png')

    def set_attr(self):
        # 窗口基本属性
        self.app_window.title('MY_GUI_APP_v1.1')
        self.app_window.geometry('960x480+200+200')
        
        # Frame
        self.frame1 = tk.Frame(self.app_window, bg='white', width=440, height=440).pack(side='left', padx=10, pady=10)
        self.frame2 = tk.Frame(self.app_window, bg='lightyellow', width=440, height=440).pack(side='left', padx=10, pady=10)
        
        # 控件
        self.canvas = tk.Canvas(self.frame1, height=440, width=440, bg='white').pack(side='left')
        self.upload_file = tk.Label(self.frame2, textvariable=self.file_path, bg='white', width=30, relief='groove').pack(side='left')
        self.upload_btn = tk.Button(self.frame2, text='选择文件', bg='lightblue', width=16, command=self.upload_on_click).pack(side='left')


    def upload_on_click(self):
        # 获取文件夹路径
        f_path = filedialog.askopenfilename()
        print('\n获取的文件地址: ', f_path)
        self.file_path.set(f_path)

def gui_start():
    init_window = tk.Tk()
    FACE_REC = MY_GUI(init_window)
    FACE_REC.set_attr()
    init_window.mainloop()

gui_start()