Profit is a terrible measure of economic activity because it is unrelated to the amount of goods changing hands. Indeed, in industries where lots and lots of goods change hands, profit is likely to be lower.

e: Also, real estate is extremely profitable, it's just not as consolidated as the major tech companies are.

If someone makes a painting in 5 minutes and another guy pays 10M USD for it very little happened. 10M changed hands and the other guy has a painting on his wall. Yet somehow income tax proponents thinks it's fair to now take 50% from that transaction just because money changed hands. It's just not a good way to organize your tax system.