But then they don't get data on which tweets you viewed.

They can't set a cookie? Associate my phone with my desktop by IP address correlation on home ISPs? C'mon, they oughta be more capable than that.

Cookies don't track you nearly as well. What happens if you delete a cookie? Fingerprinting isn't a universal solution either as iDevices all look extremely similar to each other. As to IP addresses, they only work if you connect from your home WiFi. Not every phone has that set up. Often they use carrier grade NAT so you only have a few IPs to work with.

Last, customers of their data love being able to search/correlate by phone number, not by some pseudonymous identifier that might not be present in some other dataset.

I think this crackdown might in fact be a reaction to attempts by institutions like Apple to ensure better privacy. If fingerprinting isn't giving them the data, they ask for it directly at the threat of restricting access.

>What happens if you delete a cookie?

I imagine the data of 99.9% people they mostly care about are the ones who dont know what cookies are, let alone how to delete them or otherwise mask/misdirect various internet trackers.