some details in this story https://www.bbc.co.uk/news/world-australia-63056838 have me confused. Telecoms giant hacked – millions of customers have their data acquired.

Data apparently compromised includes names, dob, addresses – which you’d prob expect,  drivers license details and passport numbers, which you maybe wouldn’t. Then its reveals peoples Medicare card info, which can be used to access health records has also been compromised.

Why would a telecoms co have this kind of personal info to lose in the first place?

its used as proof of ID over there, along with things like drivers license number. I’d assume that a large number of deals involve credit of some kind (ie to pay for your new iphone over 2 years), so identity proof is collected to assess your risk