This is why the world runs off spreadsheets
You're building all these views and processes and you get all of the problems that you would do with conventional software development, [however] you just don't have any of the standard tooling that makes your life easier while you're doing it.
So much I could write about this. Most applications used by large organisations are simply unfit for purpose. The reason that so much data is siloed in spreadsheets and sent round by email is because - shockingly in 2021 - this is still one of the most effective ways to get data in front of people that need to see it. This then introduces a massive problem because there is no single source of truth. People assume what they've been sent or have in their Inbox is always "correct".
When you have terabytes of data it goes without saying that the majority of people who use that data only need to see / work with a portion of it at any given time. A lot of these systems are designed without any consideration of end-users in mind. So when they need to get that data in front of them they simply export portions of it that are needed (even if that export involves manually copying/pasting data). They then manipulate it using Excel or some other such tool and send it on via email because, well, how else when the system itself doesn't even produce the reporting people need.
the old system could not support the new data standards, but that was never promoted to management.
Even if it was, they wouldn't care or even understand what this means. As long as it's presented as a financial figure, the lowest value will always win.
But as work began developers realised it was connected to so many other legacy systems – with little or no documentation – that this was not going to work
Documentation and handover costs money. See previous point.
This happens in _so many_ organisations it's frightening.