I have found the #1 source of architecture/reality mismatches over time being that "business" has deliberately kept developers only partially informed on a "need to know" basis.

To be clear, there was nothing malicious about it, it's just that many stakeholders only give their short term needs as input, not the long term strategy that's discussed behind closed doors in the board room. The big problem here is that non-engineers don't get that some strategies don't simply add to the problem space, but fundamentally change it.

"Why the fuck didn't you tell us sooner?" is one of the most common phrases in software development.