Plus this is a uniquely Batman idea since so much of Batman's mythos involves psychology, with an undercurrent of "Batman is two pretzels shy of Joker's Party Mix," one would assume not having his villains, the ones who affect his already profoundly damaged psyche on a very personal level, would really fuck with him.
Sure you can beat up some gangbangers or a thug robbing a liquor store, but you don't need all your fancy tech for those schmucks. You don't need all that high tech surveillance gear. You don't even need all your signature Bat tech since how many wifebeating meth-heads have access to private helicopters or some gimicky grenade launcher with a spread effect that either makes you laugh to death, freeze to death, piss your pants in absolute terror to death, or just lethally poisons you while making you smell like a chrysanthemum?
Someone's killing all of Batman's enemies, from big names like the Penguin to schmucks no one remembers like Calendar Man. Eventually they are all dead and Batman faces their killer. Said killer then shouts "Have Fun" and shoots himself in the head. All within the fist 10 pages or so.
The rest of the story is Batman dealing with the fact all his arch-enemies are dead and what that means for his overall identity. Sure he could just team up with someone else, but these were his enemies. These were the ones he fought for years. And it starts getting at him as he has an existential crisis.