Well, except you of course Brian... you seem perfectly content to operate systems with massive flaws in them just because they aren't a statistical problem yet.
Except me and millions upon millions of others. If ever there were an instance where, overall, "If it ain't broke, don't fix it," applies its with checks overall.
The perfect is the enemy of the perfectly functional, warts and all.
Massive flaws are only massive flaws when they cause massive problems on a daily basis. Hence, the checking/ACH system in the USA is not, by definition, filled with massive flaws. As I keep saying, and you choose to ignore for reasons I cannot fathom: There is virtually no business that's more concerned with preventing loss of money (and the need to reimburse, when it occurs through fault of the institutions) than banks.
The risk of checks (other, perhaps, than them bouncing) is just low. Period. End of sentence. If it weren't, the "hardening" you insist is needed would have been undertaken, long, long ago. There is, contrary to your oft-asserted opinion, "secure enough for the purposes intended."
------ Addendum ------
Credit Card Fraud Statistics ($27.86B in 2018, $28.65B in 2019, $28.43B in 2020, $32.34B in 2021. It was at $18.11B all the way back in 2014)
Check Fraud Statistics ($24 billion [estimated] in 2023, up from approximately $12 billion in 2018. There has been a
recent significant uptick, no doubt.)
Now which of those two systems is “most hardened” and which has, and has had, significantly higher losses due to fraud, year over year, for many years now?
You can’t eliminate all fraud, ever, and there are compromises made for ease of use over much tighter security. But if I have to choose which system is more problematic, and definitely in need of more attention, it’s credit cards.
But neither is being ignored. Banks do NOT like losing money. They don’t like it AT ALL. But they also realize that they have to decide when “secure is secure enough.” Perfect security would completely preclude any real ease of use. And let’s not mention that this is, and always will be, an endless game of cat and mouse. No matter what the next “latest and greatest” security measures might be (chip credit cards, anyone?) those who wish to commit fraud will surely find a way to do so.