why did the west commit to multiculturalism?

[Centurion1]

There is no country in north and west Europe with a 90% European population, with, I think, the exception of Ireland and Finland. There's none in the America's either, save perhaps for Uruguay.

Would you say then that Australia with a 90% European population is relatively homogeneous as a society? Even if one were to distinguish between Eastern and Western Europe the number would be very high.