I can go host malware on my site now, get flagged, take it down, tell Google, get my site un-flagged, and re-host the malware. Google can play cat-and-mouse with me at the expense of its users, or just keep the site flagged until enough time has passed and/or if I make enough noise about it. It's not common for a site to intentionally host malware, and especially uncommon for sites to host malware for non-nefarious purposes.