For some perhaps, it's almost a necessity. This is something entirely new, like the very phrase, 'Irish-Australian'. If you ask Australians why they're learning Irish, they will almost invariably tell you it has something to do with their origins. No doubt other motives are concealed in this phrase, motives as various as the individuals. But it's also true, surely, that it allows the expression of an aspect of identity long suppressed, and yet felt to be vital.
Few people can bear to be rootless.
We must all come from somewhere, and language is a fundamental vehicle of identity. Not many feel the need to speak their past by learning Irish, but that even a few should do so, is significant. Over 70 language are spoken in Australia, some of them indigenous, the rest imported. A few of these like Greek, or Vietnamese, owe some of their importance to the number of their speakers. But even if immigration were to be reduced, these and other languages would retain some cultural weight.