The reason why old houses do not have ground wires is because in the old days when the old houses were built there was no electrical code that required a ground wire.
The electrical codes when older houses were built does not require any grounding of the electrical system so they didn't have ground wires.
Houses built before the electrical code changed to include a required ground wire did not need a ground wire so it was not installed.
The electrical wires in those days also didn't even have ground wires like the new wires of today.
The old houses also only used the two prong electrical outlets without ground which were all that was available at the time.
The National Electric Code or NEC did not mandate or require any grounding in all electrical circuits when the older houses were built so many older homes were simply wired without any grounding or ground wires.
The absence of a ground wire is often associated with having 2 prong electrical outlets that only provide a hot and a neutral wire and no grounding path.
Having a lack of grounding wire in the electrical system can pose a safety risk and even more so with modern appliances that have metal casings which can be come energized in case of an electrical fault.
If you live in an house that has no grounding on the outlets and other electrical circuits it's best if possible to get the wiring up to code and install grounding. '
In some cases all you may need to do is upgrade the outlets and install an additional grounding wire.