Why do I have such a serious German Roach Infestation in my house?

I have been going through 1 can of Raid per month for the past few months and I am still looking at German Roaches in my house, mostly the kitchen, both babies and adult ones, I'm going to try 2 or 3 cans of Raid per month now see if that will get rid of them, why does it seem like an unlimited army of cockroaches, I keep killing and there's always more to kill.