Million+ line codebases were written entirely in COBOL.

The world advances.

Some were, I guess, but hardly all of them. The Linux kernel is built with Make, for example.

There are been several attempts at introducing a new build system, but they have been all shot down over introducing dependencies.

If it ain't broke don't fix it!

How many features could people have implemented or bugs fixed or general progress made instead of obsessing over tooling?