I have suffered through more than my fair share of those.
> I think there was a certain baked-in assumption by Kodak and others that the digitization of photography would still look a lot like how photographs were taken and shared in the film world.
I don't have any hard numbers, but at my dad's shop we probably sold and developed 95%+ negatives vs slides. We did so little E6 (much less Kodachrome) that we didn't even bother with it in-house. Most photos were shot on negative and shared as prints, not shot on slide and shared as slide shows. So if PhotoCD was supposed to take the place of a slide projector, it was already a losing proposition.
To this day, I have my favorite digital photos printed, as do my family members. There's something more intimate about passing around a photo album than sitting in front of a display.
I think PhotoCD was one of those things that was too early since there wasn't demand for sharing digitally yet, and then too late once digital cameras came out and made digitizing film unnecessary.
I actually wrote an article for CNET when Kodachrome processing was eventually shut down. https://www.cnet.com/tech/tech-industry/countdown-to-kodachr...