Maybe, just maybe, McNamara's doing the honourable thing and not picking him since he's already played top-level international RL for another country.
Like Garreth Carvell (Wales RLWC2000), Rangi Chase (NZ Maori 2008 & 2010, Exiles 2011), Michael McIllorum (Ireland RLWC08)?
I think that's enough to put this one to bed. That, and the fact he picked him last year anyway!
Honour is not the reason why he's not been picked, nor a reason why he shouldn't.
Having already played for Scotland in a World Cup ― the highest level that exists in any sport ― he shouldn't ever be allowed to switch allegiances.
Whether you think he should or shouldn't is irrelevant to the fact that it IS allowed to happen, and IS happening with other players within the very same squad (Carvell and MciIllorum), let alone other nations.
Players make their decisions within the rules and shouldn't be disadvantaged by doing what is acceptable under them rules.