Most people don't run an adblocker on their phone, and these torrent sites would cease to exist or become malware sites themselves if enough users used adblock.

Let's not kid ourselves- these site runners are not Aaron Swartz.

So what? If you are looking for an epub file, but instead get an exe just don’t run it. Mobile OSs are quite good at security, but even desktop has largely grown up to the task now.

Nobody is getting their books from torrent sites. They get ePubs or PDFs from Anna's Archive or LibGen.