OP doesn't go into details of how they check the stores, but I'd assume they have some sort of script as they checked 255k. If that's the case it would be trivial to send an automated email if malware is detected, and include links explaining how to fix it.
It won't resolve everything but it's a lot nicer than naming&shaming businesses who have effectively done nothing wrong. What I mean is they probably hired a developer or team to build their website, and assumed that they would build a secure website - they didn't go out purposely and find someone to build them a site that would be hacked.