In what way does a paycheck prove me wrong? I could just as easily argue that a good chunk of my paycheck proves that always bracing conditionals is something companies care about.

If bracing conditionals was indispensable for providing your services, I'd argue that they would.

In what way is that different for the end user compared to a closed source product with a public extension API?

We often do some profound changes to the system. This is Python, so you don't actually need to change the source, but being able to read it is indispensable. Plus, the license allows them to safely purchase our services and re-use the resulting system everywhere.