Profits are indeed increasing as a percentage of GDP.
Now what is it that we know about American companies and their profits? Something that has rather changed over the past decade or so? Yes, that’s right, we’re in a huge period of globalisation. So much so that US companies are now making very large profits outside the US economy. Apple AAPL -0.2% is making phones (or having made for it) in China and selling them in Europe. This isn’t, in any real sense, part of the US economy. Profits are being made offshore, out there in the global economy.