My following opinion is only in regard to selling yoyos privately (non-commercial).
From the buyers perspective, I agree. There are no downsides to PayPal G&S and I would not buy without it. Sure, I, as a buyer, might have to pay the fees, but that is worth the insurance, buyer protection etc. But, this is against the terms and services of PP as mentioned here already.
I also agree that if a service like PP is used, the service costs should be paid.
That said, from a private sellers perspective, accepting PP G&S bares some risks to get scammed. The buyer can just claim that the package the seller sent was empty and PP will happily return the money and the seller just lost the yoyo plus the money.
So, the reason for a private seller to prefer F&F does not necessarily have to be motivated by ill-intentions.
Would I buy privately from a seller that I don’t know in person with F&F? No, I would not. But I also would not automatically assume malicious intentions just because the seller asks for F&F.