If I were to rate and review apps as I would prefer to do, then anyone googling my name when they meet me would find my Google+ account, then it would be trivial for them to click around and find out essentially a list of all the apps I use on a regular basis, and how I use them. I don't know that there's anything too personal at the moment, but given that that information is essentially out there forever, I don't want to accidentally rate some app that might reveal my political, religious or cultural affliations (which could bias a future employer or landlord), or something else that might be very telling about my personal life.
For me, Google having a huge trove of information on me only matters to the extent that they'd ever show it to anyone else. I don't care what they do with the data internally, I've disclosed it to them, but it's clear after the Snowden documents that Google doesn't have the ability to fight government intrusion into their databases (making their huge troves a very tempting target), and after the fiasco with Google Buzz (and this nonsense with Google+ and the "real names" policy), it's become obvious that they don't seem to have the sort of mindset that is appropriate for a good steward of my private data. It's sad, because they provide many great products, but they are simply not trustworthy - as that becomes more obvious to more people, I imagine it will start to affect their bottom line.