Here’s another way to think about it.
If you’re making a small banjo, why not make it capo-ble?
The neck of a capo-ble banjo is a little bit simpler in construction than the one on a standard banjo, and therefore a little bit cheaper to make. (And lefties doesn’t require a lefty version—just a lefty nut.)
Once you’re down to 22” strings, a full length 5th string in G tuning becomes possible. Why bother with the complications of a short string?
The reviews show that short banjos can be very satisfying. That’s my experience, too. People who have tried my capo-ble banjos have liked them very much. They would surely like ones made by first-class craftsmen even better.
The advantages of the standard banjo are almost all because of its greater length. On a short banjo those advantages are gone. The short/travel/parlor banjo might as well be a capo-ble banjo, with its additional advantages.