There is a big difference between can't and won't. In the DoD case they "won't" for legal, and/or national security reasons. In the Synapse case I have no problem believing they can't because a bunch of tech "entrepreneurs" who think they can just break into as complicated an industry as money transfers are exactly the kind of people I would totally expect to mess it up without realizing it.

Most things are more complicated than people think from the outside and it's way easier to be incompetent at something than people think. That's the whole point of the rule in the first place.

I guess you are assuming that they did not employ an accounting firm or accountants to assist with the design of their system?

If that is the case (non-accountants attempting accounting, or not bothering, perhaps) then you have a point… but I doubt that is what happened.

It would be grossly negligent crossing into malfeasance, and probably criminally illegal to operate a money business without proper accounting supervision (and accounting is a regulated, qualified profession similar to law)

But, if that is indeed what happened, I look forward to seeing the founders in federal prison. I just kinda doubt they ran a banking startup without ever consulting a lawyer or an accountant.