My assumption is this is exceedingly rare, just like the Nancy Guthrie situation of aging in place and being kidnapped is very rare. The one thing they have in common besides being more vulnerable because they are elderly is money-Nancy's daughter makes many millions and the philanthropist was very wealthy. No idea if both are money related.
In terms of keeping my own mother safe, sure everyone has background checks, but I have gently suggested to her to be less flashy with her wealth. While she is miserly with others with the money she inherited from my father and her family which is her prerogative, she has very expensive jewelry, purses, etc. and she makes donations specifically to get her name out there (nothing truly charitable) and she named her donor fund after herself. I suggested to make donations anonymous, so she doesn't end up with her unusual name on plaques and lists and posted all over the internet, but this is the reason she even gives donations-she wants people to know she is rich and give her attention. Basically, it's advertising to criminals that you have a lot of money and it's not hard to look up age, addresses etc. I don't even know if it's related with the other cases, but I do think for safety purposes it's best not to make it easy for people to figure out you are rich and elderly.