Similarly on a computer, if I have all my apps in one place, all my bookmarks, all my personal data, all my contacts, etc, then this is dangerous because it's a single point of failure and malware often targets machines like this where it can see that the machine is used quite heavily by the operator and interesting things happen on it quite often. Not that malware is even the main culprit for collection. It could be just your spouse has a poke around your system for 5 minutes and collects 5 years worth of browsing history, or any other threat actor for that matter.