The Bi-Polar model is the model that the Universal Zetetic Society, which inherited Rowbotham's movement, came up with after they verified the Antarctic Midnight Sun in the 1920's; although they did not have a specific continental layout for it at the time.
Oh yes, well now, you who are so wise in the ways of science.
You made an expedition to Antarctica a century ago, so you suggest and I won't contradict. Is it too much to ask for you to make an expedition to Australia now this decade?
There is actually a Flat Earth expedition to Antarctica occurring as we speak.
I do admit that I am largely responsible for the Flat Earth Youtube community's mistaken belief that the Monopole model was the only Flat Earth model.
The media, the internet, Eric Dubey and the Youtubers got their initial information about Flat Earth from TFES, from a time before the Universal Zetetic Society materials became digitized online. Only Earth Not a Globe was available. When this website started in 2007 the goal for the first couple of years was to get and compile and understand as much as possible about the Flat Earth. The only historical information depicted it as Monopole. It wasn't until several years later, after FE Monopole was already popularized and spread on the web, did other material come online and we realized that the Victorian Flat Earth researchers moved on from Rowbotham and changed the model.
On the TFES wiki the Bi-Polar model is now taught alongside the Monopole model, depicted as the model which many Flat Earthers have moved on to. Even on this forum we find references that Lord Wilmore and Sandokhan have moved to the Bi-Polar model.
However, banishing the Monopole model would be a disservice to those who still argue for it, or use its visualizations, simplicity, or teach from it, so it stays. It stays for the same reason why Newtonian Physics stays as the main model. There is a large historical context and it exists as a stepping stone to the modern Relativity Physics which contradicts many of the Newtonian tenets.
Even when the results of the current Flat Earth expedition shows a repetition of our 1920's result that a midnight sun exists, the main Flat Earth model will still likely be Monopole. Only when the Bi-Polar model is utilized by the majority, will change occur.
After over 100 years Relativity still isn't utilized enough by the majority to become the default model that is taught. Other science theories have even taken over a thousand years to replace each other to become the main theory in their communities, so we can expect that this will take a while as well.