alt Hacker NewsCorrect, but I agree with the parent that this is a dubious case to apply that reasoning.
To make it clearer, imagine another context: "It's dangerous for a passenger to have a gun on board. Therefore, we're strictly limiting passengers to only two guns."
Like, no. The relevant sad case is present with one gun just as with two.
Of course, what complicates it is that these power banks present a small but relevant risk of burning and killing everyone on board. So yeah, you might be below the risk threshold if everyone brought two, but not three. So it's not inherently a stupid idea, but requires a really precise risk calculation to justify that figure.
That's not really how risk is managed in aviation. ICAO will have made a list of all possible ways a power bank could create a hazard. Then for each failure mode, they'll come up with two numbers: probability, and severity. There's a formula to combine those two numbers into a single risk score. Any risks over the acceptable threshold (varies depending on the circumstances and I can't remember what it is for human-rated transport) must be mitigated.
A mitigation is anything that reduces the probability or the severity of a risk. There are different categories of mitigation, some of which are more robust than others. Once the risk score moves below the acceptable threshold, the risk is satisfactorily mitigated.
Example: Rapid depressurization. Without mitigation, the risk of rapid depressurization is unacceptably high. So we mitigate the probability by requiring sensitive inspections for metal fatigue, and we mitigate the severity by providing oxygen masks, a standard flight crew procedure for making an emergency descent, and regular training on that procedure. (Plus a bunch of other things I'm not thinking of off the top of my head.)
Assuming ICAO did their due diligence - and I don't have any reason to think they didn't - they would've assessed the probability and severity of all of the ways a consumer power bank might fail. That analysis is the rationale for both the number of power banks allowed on a flight and what you're allowed to do with them. And yes, they will have considered the probability of people not following the rules (which is the reason, btw, that airplane lavatories have enormous "no smoking" signs right above an ash tray).