(Ghost Whisperer) Why did it get cancelled?

I loved Ghost Whisperer though they kind of screwed it when they killed Jim and brought him back in that ridiculous way of making his soul take over some guys body. Then Melinda got pregnant, which apparently happened before Jim died and I was happy. Then they jumped the show five years in the future and the kid was now five and the actor they got to play the kid bugged the hell out of me, I'm not the only one to think this, my mom and sister agree the kid was annoying. What do you all think got the show cancelled?