Increasing density has caused chip cost per FLOP/s to decrease exponentially over the last decades. But nowadays the price per transistor doesn't go down as fast with increased density like it used to.

E.g. new Nvidia GPUs are getting smaller for the same price, which means they are getting more expensive for the same size. At some point, the price per transistor will actually increase. Then Moore's Law (the exponential increase in transistor density) will probably stop, simply because it's not economical to produce slower chips for the same price. (Maybe the increased power efficiency will still make density scaling worth it for a little while longer, but probably not a lot longer.)