There is also the eternal rotation of the corporate wheel of centralization and decentralization, so when the official corporate HQ Oracle team inevitably becomes too slow and expensive and difficult and incompetent to deal with as part of the usual business cycle, non technical people will route around then and use Excel spreadsheets as their database, or dump json xml files into a filesystem, or use mongo primarily to keep the corporate Oracle team away, like how garlic keeps vampires away. And then when the decentralized solution falls over from poor design or lack of scalability or lack of reliability or lack of backups or lack of support personnel, adult supervision will return and there's a push to massively re-centralize into professionally engineered schema and indexes.

Another aspect of "too complex" is sometimes the true data structure of the problem is correct and also too complex. Some programmers bite off small chunks and chew on them, then push back that the entire data structure of the problem should become the small successfully chewed up chunk. A model that encompasses all of the concept of "number" is very complicated, so a programmer starts off writing a small simple integer library and pushes back that the definition of number should become the simple integer... then reality impacts and as the system evolves and demands are made, the concept of "number" needs floats, rats, complex, base conversions, maybe worse, and the original very complicated design is the only successful way to implement the business requirement of "number". Whoops. If you baked into the cake at the start how to handle rats with zero denominators life would be a lot easier and safer than bolting it on later or praying the app level code handles it, for example.