It doesn't, I was expressing my personal opinion on what kind of license I'd choose.

However, that was a bit of a non sequitur to end the comment on, my apologies.

> How would a copyleft license prevent it from being sold?

It doesn't but, it prevents the code from being sold, without the source code attached.

I can pull the code, add some levels, polish this more, call CaveRider, and sell it as a binary. With GPL, you can't do that. You need to add the source to the archive, or make it accessible without any walls.

It doesn't, but whoever sells it needs to contribute back whatever they did with it is almost as good.

It's not quite as good because some games still get griefers who sell versions on some market places without otherwise giving back to the community who maintains them.

But it's better than MIT for sure.

It doesn't, but makes it economically unviable. There's hot much point selling something your customers can duplicate for free and give to your other customers for free. grsecurity barely manages it and only because they don't have many customers and make it hard to become a customer.