You're not wrong, per se, but C++'s memory model tends to make refactoring this sort of thing a lot more painful than needed. If you introduce function you have to spend a lot of time thinking about how do the variables copy over the stack, is this data structure safe to pass to a function? And do I pass by reference? And do you return values from the stack or in allocated memory or write into a passed reference? Or do you get really gross and write a macro? And so on, until you just think "fuck it, copy-paste".

It's not an excuse, but languages definitely shape how you think, and C++ definitely encourages long functions and copy pasta.