That's really interesting. I worked in PCI (payment cards industry) and we had terminals we could relay the ISO8583 messages through, eventually opting to emulate via software for obvious reasons.
generally having to rely on a piece of hardware for high-iteration software development is very unpleasant, so my guess is they chose to abstract what the hardware would do in software for testing/development.
One of the huge pain points I was responsible for was certification of certain payment terminals. Meaning, hardcoded PANs (personal account numbers) written to magnetic stripe cards (or, worse, EMV chips) that have to make physical contact with a reader to transmit data.
Up until a point, we were able to (easily) reproduce these messages via the ISO8583 message format via software. Makes certification much more automation-friendly.
Once we got into hardware encryption/decryption via HSM devices, it wasn't as easily done.
Always so cool to hear about this sort of stuff.