This issue indeed has two sides. There's nothing to say about convenience, especially for greenfield projects or rapid experiments, where a centralized architecture is a no-brainer.

But the problems are also quite obvious, especially two major pitfalls:

First is security risks. Putting all components—including those critical modules—into the same codebase significantly increases the risk. This demands an unrealistic level of code discipline; an issue in one area can easily affect the entire system.

Second (though you didn't mention it, it should be considered) is the gradual deterioration of maintainability and scalability.