I've explained the process multiple times at length. If you want a foreigner to assimilate you have to isolate him from his own people and force him to interact and make his way among the locals, without any diaspora community or whatever anywhere near him. After a certain number of years (and under favorable circumstances e.g. political and economic stability), he will "go native." It's not like this stuff is rocket science. It's like what's even the point of anthropology departments, to yap about all the sad genocides?
"Immigrant communities" actively inhibit the assimilation process. They function as a force of foreign cultural inertia. The people from the old country, clustered together, maintain the behavior patterns of the old country, reproduce the social relationalities of the old country, and recreate the problems of their old country. Family traditions are baggage. Family history is baggage. That baggage is structural support for a self-identity and self-conception of being "built different" as compared to people around you. Communities are power networks. An immigrant community which can maintain itself through its own associations without needing to interact with and live with the locals according to the expectations of the locals constantly (not a hyperbolic exaggeration, actual constancy of necessary local interaction) is just a foreign colony in your own borders. No assimilation is possible under such circumstances, and no amount of accommodation, cultural sensitivity or concessions from locals will make it any more possible, in fact, it only entrenches the foreign culture as separate from the general population.
Cultural assimilation into a foreign country is not compatible with a country that cultivates multicultural diversity as a matter of policy. In such a country, policies of "welcoming," "accommodation" and "sensitivity" immigrants and promoting foreign cultural practices create real structural incentives to maintain such practices and to never assimilate whatsoever. If you want assimilation though, you need to throw all those ideas in the trash, and you have to stop treating immigrants as a special category of people who need special protection. If you want assimilation, the national policy for foreigners is to set an expectation upon them to comply with the norms, practices and ways of the local population, and to insist on the primacy of local culture over all others. This doesn't mean there can be no tolerance for different cultures as it's necessary when you're a player in a global economy that there will be people from all over visiting or staying for a while and they have to be treated well enough to maintain favorable relations for the benefit of the local population...
Consider this, when in China you defer to the Chinese, and they do not defer to you. If a foreigner is offended by something Chinese they laugh at you and say go away you stupid foreigner we're in China and you're not Chinese. If you're not a Muslim, you're not entering Mecca and fuck you if you think that's unfair. If you're in Saudi Arabia they cut your head off if you think you have a right to be a reddit atheist too loudly. But in a lot of countries in the west things are backwards. Locals are browbeaten to be sensitive to foreigners while foreigners are treated with kids' gloves like "cultural differences" is an excuse for violating pre-existing social expectation. What's the incentive here to assimilate under those conditions? To cuck yourself and have your aunts and uncles cry that America has made you gay? The incentive is to be as foreign as possible, because being foreign gives you power, and never be a local, because this subjects you to power.
As for me, being foreign gave me no power whatsoever when I was growing up because no one cares about a Ukrainian in 2001, there's no war, we're not refugees, and we're white. Maintaining this identity had no advantages at all, because there was also no big or strong diaspora in my vicinity... Whereas being in good standing with Americans, and being indistinguishable from Americans made it easier to live among Americans. Assimilation was rational and easy as a result. It wasn't even an intentional choice. It's an output of a process and a circumstance.
What magic potion did you drink that made you assimilate?