Google - and other Internet companies - collect data about you; that's just a fact of using the web these days. Whether it's tracking cookies, voice search results or scanning your email contents, it's a pretty big stack o' stuff, and it's getting bigger.
This data is collected for usually monetary reasons. A lot of the web is still free, and processing and reselling this data can help pay for it. Google at least provides a pretty straightforward way for you to review what they "have" on you. You can login to "My Activity" with your Google account and you can remove items if you feel the need.