Like we could choose chronological, controversial, event based, whatever, I'm sure they could be creative, some could be algorithms. They could keep the default they have now which most people wouldn't change. Then they could inject ads by whatever means they want and we could check them out or click on them or ignore them as we see fit and they could make a little money.
This isn't one of those "Why don't they just..." type posts where it's obvious why not. It's a serious question, like why can't they do this? I mean presumably there's some answer where they say that they have tested it and the current scheme increases engagement, or something like that.
That seems unconvincing though, clearly there's a problem here they are trying to address. It's a piece of software, can't they add some controls to how people use it?