Is the deficit of our public transportation sustainable?

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Roughly speaking, the Seoul Metro (subway) deficit is around 800 billion KRW. Since it is expected to easily exceed 1 trillion KRW in the future, let's just set it at 1 trillion. In fact, considering the completion of the GTX and other regional light rail lines, it will likely surpass 1 trillion.
Secondly, the bus system is also currently spending about 700 to 800 billion KRW.
Combined, that is a guaranteed deficit of about 2 trillion KRW, and this is only going to increase, not decrease. The annual budget for Seoul is about 56 trillion KRW. In that context, 2 trillion is a massive amount of money. Even though the budget is 56 trillion, fixed expenditures account for about 17 trillion. In other words, if you set that aside, we are pouring almost 1/10 of the remaining budget into this, and the deficit will only grow, not shrink. Setting aside the issue of fare hikes, I feel like they should reduce the benefits for commuter passes (Climate Card, K-Pass). It's not like we are in Japan where fares are incredibly expensive; there is no need to provide such massive benefits for commuter passes.
No matter how much I think about it, it seems impossible to maintain this indefinitely.
Actually, Seoul is somewhat able to cover this because of its high population density, but excluding southern Gyeonggi, it is obvious that all other provinces will be in even worse shape than Seoul. They are building infrastructure in the provinces under the guise of balanced regional development, but the maintenance costs for those also seem substantial.
And they aren't even being built quickly (e.g., Gwangju Line 2...)