No application is forever. Even applications that claim to be decades old, have evolved. New “norms” like the Internet connecting computers, graphical display replacing teletypes, and mouse/trackpads are among the changes that applications evolve to utilize.
Today, nothing is more important to this evolution that Parallel Computing. This is what “modernizing code” is about. The rewards can be huge for modernization of demanding applications. The penalty for ignoring the opportunity can be large too if competition takes the first step.