ShalomNewYork.com

The pasuk tells us that 3 Arei Miklat were set up in Eretz Canan and 3 on the other side of the Yarden in the land of Bnei Gad and Bnei Reuven. There were 9 Shvatim in Eretz Canan and only 2 1/2 on the other side of the Yarden, so why should the number of Arei Miklat be the same. The Gemara answers that in Gilead (which was on the East side of the Yarden) there were many killers.  They therefore needed as many cities of refuge as the 9 Shvatim.  This is difficult to understand.  The cities of refuge were specifically for unintentional killers, why would a city that has many intentional murders need more cities of refuge?
The Maharal in Gur Aryeh answers the the fact that there were many unintentional murderers in Gilead, indicates that human life was not sufficiently valued there. It stands to reason, that even those who were not murderers tended to be negligent. There were thus many unintentional killings there, as well. Revach.net