Inflation is a factor. But skimming the letters to investors these reports are based on, there’s two other big factors.
The first is that stocks became go-to investments after the crash, and prices of stocks compared to their fundamentals (the Price/Earnings ratio, etc.) are high. Lots of reasons for this (buybacks, which artificially inflate stock values; shareholder activism; ETF’s and more liquidity), but in the end there’s only so much magical thinking that makes a stock valuable when the company isn’t earning much. Even Amazon, which is known for operating at a loss, was eventually forced to make profits by shareholders who demanded it.
The second factor is that for all the America First rhetoric out there, the economy is fundamentally global. The U.S. recovered from the Great Recession enough to raise its interest rates, but many countries — including major trading partners — still feel the hangover from fiscal austerity and desperate measures to stimulate the economy. It will be a drag on growth worldwide for some time.