GDAX and Coinbase require SSN and drivers license. Why?

Why does GDAX and Coinbase require personal info like SSN and drivers license? Here's why.

Links:
https://support.coinbase.com/customer/en/portal/articles/1220621-identity-verification
https://support.gdax.com/customer/en/portal/articles/2437862-identity-verification-for-gdax-registration
https://en.wikipedia.org/wiki/Know_your_customer
http://www.cftc.gov/IndustryOversight/AntiMoneyLaundering/index.htm