The problem in my opinion is not the seasons in themselves. They make the trading game a lot more interesting and you only need one member of your realm to really worry about them (the banker). Just find someone who doesn't mind doing it.
However, that one single large geographic zone is a problem.
If the trading game was all that interesting, we wouldn't struggle to get a single Trader in so many realms, and have to go to such lengths to find players wanting to be Bankers. Most people don't what to play spreadsheet master, which is what the seasons generally require. Nor do most people wish to spend their time as Banker constantly trying to get the Lords to set up their trade offers to account for seasons. In many realms it was hard enough to get Lords to set automatic food movement once, having to adjust it even a few times for seasons can be a real headache.
