There was as much (more, even) pressure on the Italians and Irish to do the same.

But, to add to and enforce OP's point, their cultures were a larger schism away and they instead held on and entrenched their identities (to their objective detriment, no matter your moral stance). Meanwhile, Anglo, Franco, German, Dutch, etc cultures all kind of melded into the early "White American" identity; due to the general ease of assimilation.