The rationale I saw last year when they made this change was that Eliminator is a "casual" mode so you could only use your "casual" jerseys. I don't really see why that should matter, especially since they allow people to run around with beaver and moose heads in the "competitive" club mode. But people brought this up last year and again this year and it hasn't been addressed. At this point I wouldn't hold out much hope for it to change any time soon.
It's a shame too. My club never played a ton of Eliminator, but at least once a week we'd end an evening of club games by going over to Eliminator and do a single run though. It was quick, low-stress fun. The changes to casual jerseys was annoying, but the change this year to extend the games to OT if neither team has reached the goal target has made it completely unplayable for us. The first night we tried it a single game took nearly half an hour because we kept trading negative money pucks with the other team and neither team could finish the game. A mode that used to take at most 20 minutes to play now takes who knows how long. We haven't even thought of giving it another go since the first week the game came out.