Because fraud protection costs money, and it's useful to have an electronic payments medium that doesn't have it, and therefore avoids those costs.
https://www.paypal.com/us/selfhelp/article/What-are-the-fees...
> There are no fees within the U.S. to send money to family and friends when you use only your PayPal balance or bank account, or a combination of your PayPal balance and bank account.
There is scam where sellers will request select friends-and-family payments both to avoid the fee but also to avoid the protections.