There is a lot of resistance from employees not willing to change the way they work. Even seemingly simple things like standardizing language / glossary between departments so we can have a single representation in the system can be an uphill battle.
“So Oracle has this great product that will do eighty percent of what you want just by throwing the right switches in the software—no special code or anything—and it all falls down because someone asks that innocent little question: ‘What else would you like it to do?’” (p. 231).
https://www.amazon.com/dp/B00AK78QVI/ref=dp-kindle-redirect?...
But that's where the lure of the IBMs of this world comes in: they claim no change will be required, it's all free. Of course, we know that eventually it'll be a big fuckup.
I read something in a trade journal probably probably about 15 years ago, that really stuck with me: When businesses buy big software solutions (I think the article was about ERP systems), they should prepare to adjust and change their processes (within reason, of course) and not just insist that the software be modified endlessly to suit every little ossified process and preference. Not just because it's very expensive, but because the resulting system will be brittle and incompatible and taking advantage of further developments.
Too many buyers of software would benefit immensely from taking a good, hard look at those remaining 20% and making some hard decisions about what is actually important. Sure, for a government payroll system, there is limited room for movement, but I'd suspect that the majority of the long tail are people on weird, custom contracts and the correct solution is actually to hire a room full of clerks to handle these in Excel - and/or applying political pressure on the hiring parties to get their contracts adjusted to fit standard payroll schemes.