Of course they are issued at birth or when you are legally registered to live, work or become a citizen.
The card is for convenience, the id when checked by say the Police is very hard to dream up, and the naughty person riding their bike illegally on the pavement sadly gets their fine automatically, or the parent who is linked to them by.......yes you guessed it, their personal number.
Let me lay a few advantages on you:
Zero need for pieces of paper to approve anything (do you think we need our rumbelows proof of purchase for our first washing machine, or gas bill to open a bank account)
Travel to anywhere in the EU (Schengen) obviously with the card
Using any online or digital service (with bankID)
Covid pass (yes you guessed it digital with bar code, implemented in a few days)
All banking, insurances, car registration linked to it etc etc etc
The list is very long
BTW it's issued by the tax agency too, so no escaping those folks.
Maybe you can talk me through these downsides that Government will do with this data point?