Not so much that as the people with accounts probably already had their credentials stolen by some other means. Anyone dumb enough to sign up for Mac Keeper is probably dumb enough to fall for any random phishing attempt.
IE, just the other day I got a random call on my phone.
"Hi, I'm from tech support. I'm calling to help with your Windows computer. Are you the admin of your Windows computer?"
I stopped them there asking for more details (which they didn't provide) such as whose tech support. I don't doubt the next thing they would have asked for would have been some combination of my username, password, and email address.
I love getting those calls. I screw around with them. First acting all serious, like I am legitimately concerned. I ask them some questions that make them believe they're about to get some information from me, and then I drop the boom on them and tell them I'm on a Mac.