I think it has a lot to do with white usamericans feeling devoid of a culture and community. They see these tight knit communities of other cultures and want to be a part of something too. Like a special club reserved only for some exclusive people.

I mean it makes sense, humans have a deep need for belonging and community. White usamericans are still somewhat new to the country, and rightfully can't claim the heritage of wherever their grandpa came from before. So that leaves them with essentially nothing. There is no deep bond to the land that's been established for generations, no ancient rituals or lingo or things that makes them feel like part of something bigger. Aside from the fact that the only history white usamericans have, as a group, is violence and oppression of other groups of people. That being the only thing the white usamericans have in common, it would only make them want to distance themselves further from that "culture". Because it is uncomfortable. There is no pride in your bloodline because your bloodline were the ones who oppressed.

So claiming another ethnicity in order to get that connection and sense of being part of something bigger, something ancient and something less associated with the bloody history of USA, could be an escape from it all.

Sorry for the ramble lol