Python ismuch less concise at this size. Sure your algorithms are more concise, but you lose all of that and more because it you don't have 100% test coverage you never know when a stupid typo will make your program crash, while with c++ you typically can be fine with more reasonable coverage, say 80% where the last 20% is things hard to test that are unlikely to fail anyway. At that scale Python is slower to build as well because c++ lets your tests depend only one the files that changed and this your code-build-test cycle is faster despite c++ being famously slow to compile.
I see this argument a lot, but people often forget that Python is very concise (yet readable) compared to other languages.
100k LOC in Python typically contains way more business logic than C++, so it is only natural to be harder to maintain.