Now the model has broken down which is the motivation for the article. That's because the "talented" C++ developers have been hived off by the big tech firms (which can pay equivalent salaries or more), or the top video game companies (which generally pay low but make up for it in fun).
What remains are the "normal" developers. But their nature of business means you can't achieve a market edge with that level of talent, all else being equal.
This was never the case for COBOL because that was deployed to keep the business running, not for creating unique value and market edge. So "normal" developers work out just fine.
Finance firms hire a lot of talented graduates. They need to work against their natural inclinations, and provide training and mentorship to get those folks up to speed with C++; a long journey. They don't want to do it due to being seen as providing a cross-subsidy to their competitors when the graduates switch companies.