While that would also be a somewhat useful measure in this context, there's very little correlation between the size of the codebase and the size of the binary.

Programming languages and styles can vary in verbosity a lot. For example, if UEFI is written in some form of assembler code, then you quickly get a lot of lines of code while the binary doesn't grow particularly. On the other hand, high-level programming languages like Java, or even moreso functional and logic programming languages like Haskell and Prolog respectively, can generate huge binaries out of even just a few lines of code.