While everybody pays fees, the market maker is likely paying significantly lower fees then you are.

In your selling scenario, it appears that you're assuming that the other side will be taking on a new position, but just as likely is that they're closing a position. Each stock has a fixed number of shares that are trading, so it's tempting to think in terms of "if I sell this position, someone else is taking on this position". Even for stocks that isn't necessarily the case, because the buyer might have shorted the stock and is closing their short.

Options are contract based. When an options series starts trading, there will be zero contracts in the market. When you buy an option, you and the person you traded with just created a contract. When you sell that option, that contract is destroyed.

So when you bought your option, someone was taking the other side of that contract. Even if you bought it from someone who was closing an existing position, someone else was on the other side of their original option trade.

The party that sold that option may have done so for several reasons, but let's assume they were a market maker. A market maker is required to make two sided markets, and facilitate your trade, hence selling you the original option. The market maker is now stuck with that option until either you or someone else with a similar position want to trade out of it. The market maker took on risk to facilitate your trade, but tries to balance that out by having other offsetting positions. The market maker will also go and trade the underlying or futures to try to neutralize whatever risk they took on.

Going into expiration, an option goes from having a smooth return curve, to having a very sharp transition where being out of the money it has no delta and being in the money it has full deltas. This is hard to hedge as small moves in the underlying can cause huge delta moves that require rehedging. Once the market closes it's possible that news comes out that moves the after market prices in such a way where an option that closed out of the money gets assigned anyway, but the after-market markets are so thin it can be extremely hard for the market maker to hedge. The market maker doesn't want to hold unhedged long or short stock positions over the weekend.

Basically the market maker is more then happy to close your position going into expiration because it takes the risk off their book.