The selection of players for all the Countries is mostly those that have commenced, developed and played in Australia along with a smattering of English and Nz.
Many players, especially the Pacific Island countries played for Australia prior to the game expanding, the only International game was Aust v England that is all now changing and with mixed origins many players can now claim to be available to play for more than one country.
On a personal level I would think that most would support country of origin with second and third choices being swayed with own team (Knights) favourite players like hoping Ponga, Young and other have strong games in winning teams but not so much against Aust.
A lot of Knights supporters are likely attached to teams through family heritage and rightly have strong attachments to support them and any support of any team by whoever should be encouraged rather than ridiculed.