While some Apple apps install with a single purchase into both iOS and newer (M-series) Macs, other apps like Apple's Logic and iReal Pro have separate versions. This means they are optmized for iOS devices or Mac computers specifically, without making compromises. There are a number of reasons for this, for example to allow for differences in screen size, portrait/landscape UI, touch/mouse etc.
Our Mac version has dedicated key commands (because the keyboard is always attached), in the Editor—quicker edits and input using the keyboard, drag and drop (e.g. drag songs to a playlist for quick organisation, or drag a song file on to iReal Pro's icon on the dock to import) etc.
Many musicians have older Mac computers, so by us having a dedicated Mac version, they can purchase and receive the free updates, so we can support all our Mac users.