My aunt is in her 80s, no children, lives alone since my uncle passed on. We nieces and nephews feel it's our duty to keep tabs on her, and I'm always alerting her to the latest scams. It's not necessarily that she's greedy and she is savvy about a lot of things -- more so than many in her generation. But that generation and older are still very trusting. Heck, in their day, they used to leave their doors wide open even when they weren't home. So they can fall prey to anything.
Scammers also know that they can get away with their crimes because the elderly nan be too embarrassed or afraid to tell anyone they have been victimized. I think a lot of victims think if they are scammed, their relatives will try to have them committed or take over their affairs. My aunt knows that if she should fall for a scammer, she should not be afraid to tell me.