You need to understand the context here though.
It's not true that sports players from NZ and Oz can't come to the UK, the Kiwi cricketers came over, the OZ RU players came over, they're all off to Tokyo. So it's simply not true that they are avoiding this due to COVID. (They also, like utter dickheads, waited about a week after the UK decided that they would go ahead with the tournament, and then pulled out. So they showed a massive lack of class themselves).
It's (possibly/probably) not about COVID, it's about NRL clubs not wanting to have their players go to the world cup, and using COVID as an excuse. Which is frankly despicable.
It's not just NZ and Oz that will be affected, this will hit all the PI, PNG, Cook Island teams.
If the UK want to go ahead with it, they will need to have a representative Kiwi and Australian side, made up of their import players.