I suspect it comes from long experience, and that it's all about current, not voltage. Why? Because despite being isolated when these standards were set, everyone reached the same conclusion - UK, Germany, Greece, Russia, Soviet Union, Italy, Spain, etc.
I believe that's because of the relationship between breaker trip and the potential fire damage an arc-fault could do. Arc faults operate on current, and are largely voltage agnostic until the gap gets quite wide.
North America wants more power
Because of the 120 V choice, the situation is more dismal here, especially in kitchen heat-making appliances - grills, boilers, coffee makers, microwaves, etc. etc. Comparable European appliances are 2500 watts, and that is a right-size for those appliances. US appliances are clamped at 1500 watts because that is UL's limit of what they feel comfortable listing.
So if you raised American service to 30 A, appliances would immediately be built to use it all. Because a coffeemaker, grill, boiler etc. ought to be 2500 W, and so they'd simply pull 80% of 30 A, and then the question would be "why not 50 A or 80 A?"
Anyway, I don't think they'd go that way because we already have another way to do that, in reserve. We could simply implement NEMA 6-15/20 in kitchens and provide 240 V kitchen sockets. If UL allowed 1500 W before, they'd allow 3000 W here. The voltage is only 120 V from ground, but with two legs; GFCI breakers let us solve the shock problem off the shelf; and global markets are already stocked with 240 V appliances that will plug right in (they have good neutral-ground isolation because many Euro plugs are unpolarized). Honestly, this is so elegant I can't believe it hasn't already happened.
It's happenable right now; anyone with the inclination can run a 240 V circuit to their kitchen and bring in Euro appliances. It just hasn't caught on yet, but if Joanna, This Old House or some YouTube influencer started doing it, it could!
To review the basics
There are several threats against your electrical system:
- Plain overloads causing wire or device overheating and fire
- Arcing current flows (within breaker limits) causing overheating and fire
- Leakage through a human causing shock and death
In reverse order,
- Until 30 years ago they did not have an answer for the last problem, and the 1940s-1960s they forced grounding as an attempt to solve it. Now of course there is GFCI, which soundly licks the problem.
- The second problem had little solution until recently, and I think it had a lot to do with limiting current to appliances. Now it's AFCI, which are typically implemented as breakers because that gives you no-extra-cost protection of all the wiring.
- Now on the first issue.
Overloads are a real trick because you're not just trying to protect the wiring in the walls, but also the appliances that may connect to it.
That, I think, is the problem with >20 A breakers on small appliances. If that coffeemaker has an internal short, it could start a heck of a fire pulling 30-40 A, yet not have enough conductance to trip a 50 A breaker. It's my conjecture that this is why all the countries decided on 13-20 A for branch circuits.
The simple fact is, multiple circuits aren't that expensive. They were less expensive when GFCI wasn't required on all of them, but even this is easily contained if you install a subpanel and put the GFCI protection in the subpanel. And if America wanted to "get serious", they could always switch to 240 V appliances. You can right now; Code does not prohibit 240 V/NEMA 6 circuits, it only requires certain circuits be 120 V.