Because it would interfere with Google's data collection and so they don't want you to have it. Instead of having disposable browsing containers they make Chrom

Because it would interfere with Google's data collection and so they don't want you to have it. Instead of having disposable browsing containers they make Chrome itself automatically log into your Google account, then offer to continuously upload all of your browsing data via Google Chrome Sync. It's an anti-privacy user story.