[coldtea]

>This has nothing to do with tooling, but the fact that pulling the rug under an established code base could have very unintended effects, compared to simply adding and extending functionality without touching what is already there.

That's still a matter of tooling. With type-checking, static analysics, and test suites, changing code doesn't have "very unintended effects".

Back in the day, without those, things were much more opaque.