This is not perplexing but by design:
Stock market has the richest valuation in 18 years even as profit outlook worsens
Update – I see one financial analyst thinks “It’s different this time” and there is little risk of inflation. So there is that view too. Deflation is certainly likely in the shorter term due to suppressed demand (retail sales and services fell by over 16% in April).
Why the stock market rise? Probably because of future inflation. The U.S. government is printing money like crazy – calling it an “economic stimulus”.
Chart of the U.S. Money Supply from U.S. Federal Reserve:
How will these trillions in spending be paid for? Inflation.
Inflation devalues the dollar making today’s debt’s cheaper to pay off in the future. Governments have always done this. Will this be what happens this time? Who knows for sure?
Inflation taxes everyone simultaneously by lowering the purchasing power of the dollars they hold.
As this chart of the M2 Money Supply highlights, the rapid rise (and that is only through April 27th – not May 13th – today) may lead to inflation. (Chart from ycharts.com)
In a high inflation environment you do not want to own lots of cash. Instead, you should be buying “stuff” that you plan to buy anyway, sooner, rather than later, as it will cost more in the future due to inflation 
Next, you should invest in things whose value will remain the same as the dollar depreciates in value. For example, real estate. Due to inflation, the $100k home you could buy today for $100k becomes $150k after 50% inflation. Another way to look at is that after 50% inflation, each dollar no longer buys $1.00 but instead buys $0.67 worth of stuff – so you need to spend 150,000 x $0.67 to buy that home in the future rather than 100,000 x 1.00 today.
Some will buy commodities but those, such as gold, do not pay a dividend or provide an income return.
Holding debt is also good in an inflationary environment since today’s debt will be paid off in future inflated dollars. Let’s say you borrow $50,000 today and make $100,000 per year in income. At some future time after 50% inflation, your debt is still $50,000/year but your income has increased to $150,000 due to inflation. You are now paying off that $50,000 debt with future dollars. It’s hard to wrap your mind around it but the value of the debt, as a monetary instrument, is higher after inflation.
Holding stocks – which represent real things – is also a decent strategy as the valuation will tend to rise along with inflation. Sort of like the owning of real estate example, above. But now you own a tiny part of someone’s factory or office complex or brand value. Those “things” will rise in dollar terms during inflation.
Of course, investing in “stuff” in this environment is not risk free. If you hold cash, you will have a guaranteed loss equal to the inflation rate. If you purchase real estate or stocks or debt, you will also be taking on the risk that they go down in value for any number of reasons. With real estate, you do have some control over the property (say a rental, which you can improve over time), but with stocks you rely on third party company management to run the business effectively. Regardless, “stuff” will fluctuate up and down in value, but hopefully in a wobbly line that over time is increasing.
The stock market’s valuation may have gone up as unemployment has skyrocketed because investors think the government is manufacturing inflation causing “things” a.k.a. stock shares to rise in value. Eventually the economic disaster will gradually recover too and there will be an increase in demand for goods and services.
 In the short term, some goods and services have dropped in price – that’s deflation. Oil-based products are less expensive right now, for example. But many food items have gone up in price too. As long as people are kept under house arrest, overall demand goes down and prices may drop too (but not beneath the minimum floor at which businesses go bankrupt). In 6, 12 or 18 months, more people are working and demand feeds the inflated money supply into higher prices.