That is the bonkers thing about this story. Why take on the liability? Get what you need and toss the responsibility. If you must store it (which seems unlikely) put that extra-bad-if-leaked information behind a separate append only service for which read is heavily restricted.
Because it's free training data and great for building profiles on users so you can make money showing them targeted ads
The data is valuable to sell or train ai on. You can use that data to train ai hr people or whatever
Because there is no liability.
If they were fined $10k per leaked ID, then there is a serious liability there.
Right now, they publish a press release, go 'oopsie poopsie', maybe have to pay for some anit-fraud things from equifax if someone asks, and call it day.