These sites are notorious for "malvertising." Clicking a download link often triggers pop-ups that can install spyware or ransomware on your device.
But as a consumer, the risk often outweighs the reward. The potential for legal notices, the definite risk of device malware, and the moral question of robbing filmmakers of their dues (even bad movies) makes the 300MB path a shaky one.
The truth is, the is slowly dying. Two factors are at play: