I can't speak for everyone, or even the majority, but I know that oftentimes large projects focus on build times, undergoing refactorings as you describe, and t

I can't speak for everyone, or even the majority, but I know that oftentimes large projects focus on build times, undergoing refactorings as you describe, and their compile times are still high. To make up some numbers, maybe the fraction of projects that have unacceptable compile times could be reduced from 80% to 40% (at what effort?), but that 40% remainder probably includes many large, popular crates.