https://www.techradar.com/news/apple-users-dont-want-macos-and-ios-merged-tim-cook-says

Apple CEO Tim Cook wants to politely squash any rumors that Apple’s iOS and macOS operating systems will merge into one at some point in the future. Speaking to The Sydney Morning Herald during Apple's Chicago New iPad for education event, Cook said he doesn’t think users want the two OSes to merge.

“So this merger thing that some folks are fixated on, I don't think that's what users want,” Cook said. He also alluded to the fact that while merging would make the company more efficient, it would be at the cost of lost features uniquely built to the hardware involved.