It's possible Equifax was the only credit agency with enough information to require public disclosure... if Transunion doesn't have the right logs or monitors, they may never find out they've been breached, and nor will we.
At this point, I assume everything on a computer can become public.
One of the few times I don't enjoy been right, I'm fortunate in that I'm vanilla, FSM help people under repressive regimes or who hold opinions that worry those in authority wherever they are.
We managed to combine a panopticon with a Skinner box somehow and people like it because it's shiny.
So, your last sentence is true.
However, there are ways to secure things in a practical manner and ways to detect, and stop, intrusions - though those ways look nothing like they do in the movies.
There are practical ways to limit exposure and to make data exfiltration more difficult. There are layers and practices that can be put in place to make it more difficult to do and easier to notice.
They are expensive and they do impact efficiency and may impact efficacy.
The easiest way to avoid data exfiltration is to not store it in the first place. But, that means they are less able to track the consumer and then less able to do effective targeting of ads and things like that.
The bottom line is it is expensive to reasonably secure your systems and the penalty for not doing so is less than the profits being made from not securing their systems in a reasonable manner.
Without larger penalties, this is unlikely to change. Maybe, just maybe, enough people will be impacted to where they actually start imposing serious penalties for negligence or willfully neglecting security. Maybe...
Abstract: In this bleak, relentlessly morbid talk, James Mickens will describe why making computers secure is an intrinsically impossible task. He will explain why no programming language makes it easy to write secure code. He will then discuss why cloud computing is a black hole for privacy, and only useful for people who want to fill your machine with ads, viruses, or viruses that masquerade as ads. At this point in the talk, an audience member may suggest that Bitcoins can make things better. Mickens will laugh at this audience member and then explain why trusting the Bitcoin infrastructure is like asking Dracula to become a vegan. Mickens will conclude by describing why true love is a joke and why we are all destined to die alone and tormented. The first ten attendees will get balloon animals, and/or an unconvincing explanation about why Mickens intended to (but did not) bring balloon animals. Mickens will then flee on horseback while shouting “The Prince of Lies escapes again!”