Не следует создавать новый Listbox
для каждой строки файла.
from tkinter import *
top = Tk()
lb = Listbox(top, width=100, height=40)
lb.pack(side=LEFT, fill=BOTH, expand=1)
sb = Scrollbar(top, orient=VERTICAL, command=lb.yview)
sb.pack(side=RIGHT, fill=Y)
lb.config(yscrollcommand=sb.set)
with open('new.txt') as f:
for line in f:
lb.insert(END, line)
top.mainloop()