[jongjong]

Yeah it's a case of falling in love with the solution, not with the problem.

The real reason for tight coupling is simply complex interfaces. That means a range of things; complex function signatures which rely on highly specific parameters (e.g. live instances instead of raw primitive values or raw data) or return complex values instead of raw information "here's what I did". It can also mean complex API parameters and response payloads. Ideally, complex processing should be hidden behind simple interfaces which don't encourage micromanaging the module/service. If the interface is as complex as the processing behind it, that's a design failure and will lead to tight coupling.

Separating code into modules and services may be intended as a way to encourage developers to think about separation of concerns so that they may end up designing simpler interfaces but it doesn't seem to help certain people. Some see it as an opportunity to add even more complexity.