The same reason you call someone an idiot if they click an ad that looks like an error message, login to their bank on mybank.com.sketchysite.info, respond to a Nigerian scam or open that .pdf.scr file attached to an email. This stuff seems dead flat basic to people who are exposed to scams regularly. We don't call the scammers idiots for making millions on ransomware, most of us just delete their messages without a second thought - instead we call their victims idiots for falling for it in ways that seem obvious to us. Heck, even in much of the general public these are used as punchlines on occasion. Victim blaming and just expecting people to recognize these things as sketchy seems to be quite common for these sorts of technical issues.