Profits are unusually high almost entirely due to two factors. First, the massive expansion of the global economy the last ~20 years has particularly benefited the top Fortune 500 companies, along with the artificially cheap dollar from ~2003-2014 (which has now reversed and is wrecking profits for that same club). The global economy has grown far faster than the US economy since the late 1990s, companies that had exposure to that were obviously going to benefit tremendously vs domestic oriented companies. Second, the substantial margins and profit of the top US tech companies, which have boomed more than any other companies over those 20 years.

Apple, Microsoft, Google, Oracle, Intel, Cisco, Qualcomm, etc

That's about $130 billion in profit, between those seven companies.

Oracle produces five Caterpillars worth of profit.

Apple's profit is nearly Berkshire Hathaway + Johnson & Johnson + Boeing + General Electric.

Or even more dramatic, if you were to do a three year average on profits, Apple would just about add up to these companies combined:

Union Pacific, Visa, 3M, Caterpillar, McDonalds, CVS, Walgreens, Costco, Target, Honeywell, GM, Ford, Lockheed, Boeing, UPS, Fedex, Delta, America Airlines

Microsoft is Goldman Sachs + Disney + Procter & Gamble.

Google's profit is roughly greater than the top 50 US defense contractors combined. You might as well just say it's equal to the entire US defense contracting industry combined.

Now strip out just Apple, Google and Microsoft, and then inflation adjust the remaining Fortune 500 back to a 1995 dollar and compare the group with the Fortune 500 of the mid to late 1990s. What you'll see, is US corporate profits are not that unusual and the top tech companies are producing a very large warping of the picture.