This seemed surprising to me on the first read, but it makes sense. An average senior software engineer probably makes ~$120K in US. They often work on systems

This seemed surprising to me on the first read, but it makes sense. An average senior software engineer probably makes ~$120K in US. They often work on systems that aren't in any way critical and are more or less replaceable. Anything in COBOL these days is by definition is crucial and highly expensive infrastructure. The talent pool to work with that tech is small. They are by definition very experienced and probably highly specialized even within that pool. So upper six digit salary actually makes sense. To be honest, the idea of companies paying through their noses because of decades of short-term thinking makes me smile. Karma in action.