yes there is a reason why you can only download slower than you upload. perhaps it is due to the fact that the other people that you are downloading from have a limited amount of bandwidth and they are sending to you as fast as they can.. or perhaps the connection between you and them is slower than the connection between you and the person (s) downloading from you. this is a very common thing in filesharing with people who have lots of bandwidth. but please be patient and share your bandwidth. only the users of the network can increase its speed.
thats all im off my soapbox now