If a fixed cost does not change as output changes, why do you still have to pay it if you produce zero output?
Answer: There are some inputs that you must commit to just to get into the market. For example, you may need factory space. You will have to sign a lease or a loan agreement to get access to the space. The owner of the space or the bank that lends you the money does not care how much you produce. They must get paid every month no matter what. You may have to pay out of your own resources if you produce nothing.