Haven't airlines always mostly tried to look like one another?
When I was very small, all silver.
Then along came a white top with a cheatline, just BOAC & TWA having unconventional cheatlines.
Then the cheatline got swept up to end at the top of the fin.
Then the white top spread downwards and the lower part of the fuselage was coloured - or the other way round.
Massive overgeneralisations I have no doubt, but there such a thing as fashion, and if an airline says, we want to be fashionable, then their design consultants will offer something like every other fashionable airline.
Two words; "Marketing Consultants"!!