[rubber_duck]

I don't know enough about Excel but I highly doubt it's about the looks - I have Office installed on my MBP and the ribbon looks like I remember it from Windows.

I don't understand your point - non-native widgets are not a deal breaker and there are plenty of examples, Electron being the most common non-native cross platform framework recently (it has technical limitations but even the subpar performance doesn't make it a deal-breaker). So it's possible to create cross-platform UI frameworks and most of the the most successful apps I can think of are using some version.