Wait, what? 100k+ LoC is more like a "two-pizza" team and a few years, empirically. And this is in C++, a language where LoC don't flow nearly as quickly as in other languages. Even extremely complex code bases (think database engines) are entirely manageable at this scale and beyond without introducing microservices. Monoliths will scale into millions of LoC with little loss of effectiveness if your code base and processes are setup correctly.

You are describing the consequences of poor architecture and process, not anything intrinsic to software projects.