There are several reasons for the economic upturn in the United States since 2016. One reason is that the economy has been in an upswing as it is recovering from the recession in 2008. In the 8 years since the recesssion, the economy has been recovering. This is due to careful strategic planning at the Federal Reserve and other major financial institutions.
Another reason the economy, and especially stock prices, have seen a jump since 2016 is that President Trump is widely seen as pro-business. When Trump was elected some businesses saw this as a promising sign for business-friendly policies in the future.