Having discrete jumps on a mechanical analog clock is not a particularly hard problem. Certainly easier that shrinking an accurate mechanical time keeping device down to wrist watch size.

For that matter getting a purely digital display out of a mechanical clock is not diffucult either either.

If there was a strong demand for such a product, they would have caught on before the 7 segment display made them the cheapest option. Possibly as a luxury or status symbol depending on how the cost worked out.