Don't see how this is relevant to the thread, but people of the same rating are ranked by age (older ones are ranked higher).
So the first person goes at 250. Then everyone else goes down, from 250 to 1250. That leaves 750 of the people out of bronze.
Then, the people in the top 250 start losing, getting ratings under 0, putting them below the people who have a rating of 0. They end up in like 1250ish rank.
Meanwhile, the first person (at 250) goes up one rank per everyone booted below a rating of 0, slowly getting closer and closer to the top.
If they lose once, then they get a rating less than 0, and get booted to below 1250, allowing the people below them to move up.
And slowly, at a rate dependent on how many people are playing arena, everyone will have their chance.