iPads already outsell Macs. I imagine Apple is willing to accept lower margin overall for iPad hardware (vs. Mac) since it gets a cut of iPad software sales on the App Store. This is perhaps a business reason for why you want macOS on an iPad and Apple does not.

However, Jobs also believed in product differentiation and thought that having too many products in the same space was confusing. Arguably by making iPadOS more macOS-like Apple is reducing that differentiation and increasing confusion.