Why are people buying/selling out of the money calls and puts with just a few hours left until expiration

I sold some puts that expired last Friday. They were out of the money (good for me) and had a .03 cent price. They weren't so far out of the money that there was zero chance of them being exercised. I was interested to see what would happen if I tried to buy to close. To my surprise they sold right way. So somebody got $3. I guess if you do enough of that you can make some cash so that makes some sense. But is there really enough of a market for them to make it worth it?

I've seen it the other way as well where I sold to close way out of the money calls right near closing. That seems even more curious to me because they were guaranteed to expire worthless. Are people just buying them and selling them right up to the last minute in hopes they won't be the one holding the hot potato?