Wouldn't say it was just a software glitch, bureaucracy tried to cover it for bad press at all levels in the government ran agency.
As you said this didn't just involve software issues to get that big, but I still wonder how all the devs that worked on this over the years could just shrug it off all these years. You can't tell me not a single dev got wind of these issues. Did they just immediately jump to "impossible I'm the most awesome person on this planet no way there's a problem these people all just stole money". I'd have sleepless nights going over the whole system in my mind trying to figure out where things went wrong. Is this some sort of dunning -kruger going on? I don't really consider myself a coding wizard or anything, but I think I know about enough to know I'll keep producing bugs til the day I die. Rust won't stop logic bugs from happening.
They told every single victim "you're the only one who's claiming there are issues".
"The Post Office is owned by the government, through the Department for Business, Energy and Industrial Strategy (BEIS) and UK Government Investments (UKGI), however, the Post Office Ltd Board has responsibility for the operations of the Post Office" [0]
And "The Department of Business Energy and Industrial Strategy holds government responsibility for postal affairs, including the Post Office" ... "the Post Office Ltd remains accountable to the government" [0]
[0] https://researchbriefings.files.parliament.uk/documents/CBP-...