Elmwood,
Do you have any info about where geographically you’re seeing this?
I agree with Mangetout in general, but having lived all over the USA I’ve also noticed that it varies greatly by geography.
In particular, it seems that in NYC folks stay very close to their heritage and you’ll see 3rd generation native-born americans still speaking the ancestral language and having a distinct accent.
The same thing is exceedingly rare on the West Coast.
That doesn’t answer why Italian-Americans (“IAs”) seem to you to be different from other groups.
Perhaps the other groups are even more insular, and as a result tend to gather at ethnic-specific dating sites. The IAs, OTOH, are too mainstream for ethnic-specific sites, so you see them at general interest sites. Meanwhile they still see themselves ethnic enough to want to date within the group.
You could also view this, paradoxically, as a sign of their acceptance within the larger culture.
[preparing to tread lightly]
If, for example, a Black or Jewish person insisted in their profile that they wanted to date only more of the same, that could be seen by the public at large as quite ethnocentric bordering perhaps on mildly racist. It certainly sounds separatist.
But for an IA, since they’re (in my supposition) more fully integrated, the sting is drawn. It lacks the racist overtone and sounds a lot more like a mere harmless personal preference.
So as a result, IAs are not as inhibited about making the preference public. the other groups may have the same-group preference even more strongly, but they’ll be quiet about it until they’re emailing one-on-one.
Again it’s just a theory, and an amateur one at that.