That's an excellent question!
Sound on film is rare. Optical sound on film is the rarest of them all — a relic of a bygone era that was niche in its own time. Unfortunately, it is not something we are currently able to process.
Optical sound for 8mm and 16mm film was a method of sound for commercial releases of films. It was more popular in Europe than in the USA, and primarily saw usage on airlines up until the 1990s. If you flew on a transatlantic flight in the 1980s, the chances that the inflight movie was Super8 film with optical sound are pretty high.
Film with optical sound was much easier to duplicate than film with magnetic sound, which is was why distributors of commercial films used it. However, the sound quality was generally worse than magnetic sound. It also required specialized equipment to use in the home, which most people were not willing to invest in, especially due to the advent of more popular, easier to use formats like Beta and VHS.
Since optical sound is so rare — optical film in good condition is even more of an anomaly — and to ensure we’re providing the highest quality transfers, it is not our standard process to digitize film with optical sound.