To be fair I think that is literally what they are trying to do with this proposal, it's a sloppy attempt but still I think that is what they are attempting...
The problem with playing games in Tonga aren't just commercial ones, there biggest stadium (and the only one that we'd really recognise as a stadium) is Teufaiva Sport Stadium, it's a multipurpose stadium with 10 thousand seats and basically none of the facilities necessary to host a game, even if we ignore that it'd be a chore to get it in a position where it could broadcast games to a standard that the audience in Aus, Eng, and NZ would expect, for the players it'd be like going back to when they were playing under 6s with the lack of facilities for them as well. It's also in a state of disrepair after it was damaged in a cyclone earlier this year (and it wasn't in very good condition beforehand either).
So yeah I can understand why playing games in Tonga is an issue, it's a similar situation in Fiji and Samoa though you could pull it off in Samoa and Fiji from time to time, but for PNG there's no excuse games should be played there regularly.
Lobbying the Aus and NZ governments for support to upgrade Teufaiva, Apia Park, and ANZ (Fiji) would be a good start for getting those nations in a position where they could host games regularly, it'd only cost a few million each to get them to a place where it's workable as well, and both governments waste international aid on much more frivolous things anyway.
On NZ, the only reason that more games aren't played in NZ is cause the NZRL don't organise them, they don't even try to organise internationals independent of either the NRL or RFL and haven't for a long time.
And again to be fair I don't think that the NRL's proposed schedule was intended to be a comprehensive international calendar, I think it was just a proposal for the events that they would take a part in organising or they'd be participating in some way with, hence why no schedule for Wales, Scotland, France, etc, etc.
