Comment by amiga386

In the 1980s and 1990s, there were a number of commercial Unices (SunOS, HP-UX, AIX, IRIX, etc.) Every one of them was incompatible with each other, sometimes subtly, sometimes blatantly. They were all competing against each other and all seemed to encourage you to use their proprietary extensions in your software and deliberately fuck over anyone using any other variants.

What it meant was a headache for writing platform-agnostic software. It was not a productive way to create software.

Replacing GPL software with MIT software just encourages this behaviour to come back. We already see it with how macOS userland took FreeBSD and sprinkled incompatibilities everywhere.