Sue Dibney and Jean Loring were both publicly known to be the partners (or former partners) of superheroes. Lois is not publically known to be Superman's wife, but as recent events in Superman have shown, she's known to be associated with him and many people assume that relationship to be extremely close. Sue and Ralph were the object of books and TV movies; Jean Loring's divorce made the cover of PERSONS magazine. Superman and Lois have shared a great deal of publicity over the years, with Lois writing much of it.
So who the hell is Jack Drake?
Jack Drake is a nobody. He has no publicity, no recognized link with the hero community. His only claim to it is that he's the father of a sidekick, a hero whose name is best known, as Dick Grayson once put it, as the back end of "Batman and..." -- but Jack only found that out recently, and if not for recent events in Robin, Jack wouldn't even have had any clue why somebody might be coming to kill him.
I have thoughts on why Boomerang would target Jack, against his controller's wishes. First, my guess on how he pulled off the murders beforehand.
Ollie refers to the security systems that protect the heroes' homes as including multiple types of countermeasures. These include Kryptonian technology and Martian tech, "plus that really scary crap that Bruce invented."
Captain Boomerang has been using the M.O.s of his fellows in the Suicide Squad.
Who else was in the Suicide Squad?
Here's my guess: Suicide Squad, or its remnants, has access to Batman's files. I'm guessing via Oracle, given her past relationship with the squad. [Edit: obviously, I don't mean that Oracle's in on it -- I'm saying that someone got access to Batman's files through her.] Including schematics of the security systems.
What do you want to bet that Batman left himself a back door in the part of the security system he invented? One that nobody else can pick up on? One that lets him come and go as he pleases without detection -- just in case?
Meltzer has said one part of IC is taking Batman down a peg. That'd do it.
That also explains how Jack's identity got out. It's in Batman's files, too. As for why -- I think Captain Boomerang specifically wanted to strike a hero's father. Because he was surprised to find out his son has super-speed.
The son's immediate reaction was to question whether Golden Glider was, as he believed, his mother. To which Captain Boomerang's reply was "...No." Which made some folks speculate, and one thing was obvious pretty quickly: there's a dearth of female super-speedsters, especially in the right age bracket.
Which means Cap's son got his speed from his father.
Which means the father isn't Captain Boomerang.
Which gives Captain Boomerang a reason to want to work out his frustrations on Jack.
It's a thought, anyway.