Read the article... this isn't just people suing because they didn't read the disclaimers in incognito mode.

The lawyers spearheading the lawsuit have already amassed a trove of internal Google emails they say show how the company’s executives have known for years that what the company calls “Incognito mode” is anything but incognito. Private browsing modes usually block tracking cookies — little bits of code that follow people around the internet logging their activity.

But Google still logged information on people using private mode whenever they visited websites that had installed hugely popular Google software used for serving ads or measuring traffic, the lawsuit alleges.

It sounds like Google was disabling 3rd party cookies in Incognito mode, but conveniently allowing its own to remain.