I'm pretty sure scrutinizing your browser history is still extremely valuable. But I find it quite plausible that email in particular has lost value as marketing information.
People still use email for all kinds of business, of course. But their day-to-day personal activities, the kind that marketers care about ("I've taken up kayaking!", "I'm pregnant!") don't usually show up in emails any more, they get posted on social media.
People still use email for all kinds of business, of course. But their day-to-day personal activities, the kind that marketers care about ("I've taken up kayaking!", "I'm pregnant!") don't usually show up in emails any more, they get posted on social media.