As of version 69, the Chrome browser will log you in and sync when you visit any Google site like Gmail, YouTube, Google Docs, Google Maps, etc. For whatever reason, you may not want to be logged in, or you may not want them to keep track of everything you do. They are not giving you that choice anymore.
There was a discussion on Twitter about it with Adrienne Porter Felt, a Chrome engineer and manager.
Apparently after these discussions and feedback, Google is going to back down and make some changes come version 70 coming out in mid-October. They will allow sign-in without syncing. If you want to sync between devices, you will need to turn sync on. Signing into a Google owned website will not sign them into Chrome at the same time.