So what's the reason for not extending these protections to all?

There’s no risk. The likelihood that my conduct at work will attract an assassin is zero.

I’m probably more likely to choke on a pretzel.

Then covering you too would be an approximately zero cost to that law. Yet it would cover retired judges, nearly-judges, people who aren't judges but have similar problems we haven't thought of yet, and have the moral advantage of treating everyone the same.

That's just a reason why you aren't supporting the protections for everyone. What's your reason for opposing it being applied to everyone?

Just because you feel there is no risk of a disgruntled person targeting you, doesn't mean that there are other people who don't have risk in other jobs (like doctors or managers).

Not everyone has the same risk of being robbed. But laws against robbery need not offer unequal protections to victims.