What a completely random thing to do.

It makes sense to me. Biden and Trump have Secret Service detail already. RFK does not. Biden wants to make sure that it at least looks like all 3 candidates are being protected from more violence.

But why JRFK Jr and not Jill Stein or Cornell West?

Because neither of them have polled high enough to qualify for it, neither has the libertarian candidate, even RFK Jr. wasn’t polling well enough for it, which is why Biden had to order this, and it wasn’t done automatically.

He’s also a Kennedy, so his chance of being assassinated is probably higher than your average candidate.

Assassination is hereditary!?