I feel like it makes sense to use COBOL to talk to a government mainframe that’s likely also using COBOL, and likely has a wire protocol specced as a set of ready-to-use COBOL client structs.

Sort of like, in the modern day, it makes sense to use Go if the goal is to write an adapter that takes stuff from your database and pushes it out to some remote consumer that speaks ProtoBuf, and has a ready-to-use ProtoBuf schema.