Hi Welcome to the forums
You have to realize that you are often downloading from hosts who have a much slower speed than you. If you were downloading from me you would not get higher than 50 KB/s on a good day, and if I was not uploading to anyone else. I set my max uploads to 5 and so this would mean that you might only get 10kB/s off me. Some people set their limits way to high which meand you would get even slower speeds.
If you are getting a file of multiple hosts, they may not all actually be uploading and they may all be very slow. Even a T1 or T3 host will oftan give very low speeds, depending on how they are configured.
The main thing is to realize that your speed will be governed by the other host if they are slower . I hope this helps