There’s a huge amount of risk in rewriting old code. That COBOL or FORTRAN code is likely rock solid and has had 50 years of bug fixes applied to it to cover every possible edge case.
It’s hard to justify the expensive of rewriting all of it (which would likely cost tens of millions of dollars) if the result is new code that does exactly the same thing as the old code.
There’s a huge amount of risk in rewriting old code. That COBOL or FORTRAN code is likely rock solid and has had 50 years of bug fixes applied to it to cover every possible edge case.
It’s hard to justify the expensive of rewriting all of it (which would likely cost tens of millions of dollars) if the result is new code that does exactly the same thing as the old code.