Earlier quoted context omitted.
Considering you cannot use cookies for mobile traffic, it's understandable that most firms are moving away from it. Fingerprinting and device IDs have been common for a few years and I don't think it will go away any time soon.
Why can't you use cookies for mobile traffic?
This becomes important in the context of third party cookies that want to track you across apps. Hence why cookies are not a reliable method of identification on mobile.
Hope this clears it up. :)