使用pyAesCrypt加密文件时，pyqt5 gui为什么会滞后？

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton, QFileDialog, QLabel
from PyQt5.QtCore import QThread, pyqtSignal
import pyAesCrypt

class EncryptThread(QThread):
    progress = pyqtSignal(int)

    def __init__(self, file_path, password):
        super().__init__()
        self.file_path = file_path
        self.password = password

    def run(self):
        buffer_size = 64 * 1024
        with open(self.file_path, 'rb') as f_in:
            with open(self.file_path + '.enc', 'wb') as f_out:
                pyAesCrypt.encryptStream(f_in, f_out, self.password, buffer_size)
                self.progress.emit(100)

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        self.setWindowTitle('File Encryptor')
        self.setGeometry(100, 100, 300, 200)

        self.button = QPushButton('Encrypt File', self)
        self.button.clicked.connect(self.encrypt_file)
        self.button.move(100, 80)

        self.label = QLabel('Progress: 0%', self)
        self.label.move(100, 120)

    def encrypt_file(self):
        options = QFileDialog.Options()
        file_path, _ = QFileDialog.getOpenFileName(self, "QFileDialog.getOpenFileName()", "",
                                                  "All Files (*);;Python Files (*.py)", options=options)
        if file_path:
            password = input("Enter password: ")
            self.thread = EncryptThread(file_path, password)
            self.thread.progress.connect(self.update_progress)
            self.thread.start()

    def update_progress(self, value):
        self.label.setText(f'Progress: {value}%')

if __name__ == '__main__':
    app = QApplication(sys.argv)
    mainWin = MainWindow()
    mainWin.show()
    sys.exit(app.exec_())