Little Correction: not by the average web engineer.

This is a very true statement.

I laugh at how the only thing discussed here is open source software and the cloud. People forget that there's a whole entire world of enterprise software and systems.

As someone else mentioned earlier, mid to large size companies don't replace systems like people do here with Javascript frameworks. It is really expensive and costly to replace systems that have been around for decades. The business logic tied up in some of these systems is so vast and complex that it is cheaper to keep them around than to replace them with something new.

I would restate it that there is deep business logic encoded solely in a system that grew organically over decades. It's not always that it would be hard to rewrite it all... It's that no one knows or has documented anywhere except this organic code base all of the requirements. And specifically no one has encoded WHY.

So rewriting and keeping the same logic is very difficult and the business risk is very high due to all the unknowns: features, time, compliance, correctness, performance.

Sure it is.