Not really mentioned, but I suspect that at least part of the time, the leaky pipes are caused by the trees. I used to own a house in southern California with a sprinkler system and a couple Chinese elms. Trying to track down why some sprinkler heads weren’t sprinkling, I discovered that the trees had sent roots into some of the (PVC) piping, going as far as six feet of the pipe. I ended up digging up and replacing a lot of piping on that project, although I wouldn’t be surprised if the Chinese elms (which are nasty nasty trees that I will hate until I die) didn’t pull the same stunt on subsequent owners of the house.