read the report https://transparencyreport.uber.com/
the 12M users are mostly demands from regulatory authorities
- 6M is California, likely CPUC
- 3M is New York, probably the TLC there
that's how you get the data sets for analysis like http://toddwschneider.com/posts/analyzing-1-1-billion-nyc-ta... which appear on HN periodically and are eagerly upvoted
the regulators make this a requirement for Uber to open or continue operating in their respective regions. Uber tries to negotiate a narrow scope for info disclosure as much as possible.
(disclaimer: uber employee)