I really don't see the issue. There is no point comparing this to other World Cups in other sports.
You can never compare like with like when comparing competitions.
RL is what it is. It can only do well compared to it's own standards. Admittedly they are lower than what we would want, but wishing it does not making it happen.
There are a few polls on different sites and there are still a lot of people yet to buy.
In games like football, people have to buy ahead, or they would miss out to the richer folks who can buy ahead.
In RL, because the spectator population is smaller, the quantity of those with enough spare cash to buy ahead are smaller.
I'm sure there will be some walk ups for some of the matches, but I can't see many walk ups for a game a Wembley. If you are travelling distance you are going to want a ticket in advance, but in this day and age, I would not buy more than a couple of weeks ahead for anything. Even my daughters Birthday party which as a family comes in way ahead of anything RL wise, was booked with only a few weeks to spare, and places for those are far more likely to sell out.