Having things totally separate means harder to enforce quality controls.
Madness string 24890
The safest course was actually the simplest - do nothing at all and hope everything turned out for the best. It wasn't a great plan, but it had the benefits of simplicity and a long tradition.
Bad code is truly like cancer. People start building on it and irresponsibly adding it as a dependency, and eventually, removing it is like chopping off an enormous tumor. It's an operation so severe that a lot of companies won't live through it.