I have a similar question / issue. I use iPhoto and have for years. My wife has a newer 2017 MacBook Air how do I get iPhoto for it? I will soon be buying a new laptop and will need to put iPhoto on it or buy a replacement software package (Lightroom?). So I want to know if I can continue using iPhoto?
Thanks! It's good to hear that it can still work with Mojave.
Now as for why iPhoto and not Photo's; very simple I use iPhoto primarily for photo management and to a lesser degree for photo editing. I don't need better editing tools the iPhoto ones work OK for me. So it come down to photo management. The most most most common command I use in iPhoto is the batch command to add/change titles and descriptions to photos. When Photos first came out they had no such capability. Years later I found out how to do it in Photos but it seemed difficult and still not worth using. The last time I tried photos I could not figure out how to do this again. Tell me how to do this as simply as in iPhoto and I will gladly switch.
Jim