Its just a conspiracy theory but I don't see much people are selling their shares to buy cryptos and bitcoins, now only people started to see it as an alternative to traditional investment so it will take lot more time for people to get convinced.
We will not know who are those people are selling stocks.
Financial institutions are starting to see the importance of bitcoin. They're being aware that it could be big as they could imagine.
And I don't really want to stocks to go down and it won't go either because without any economic activities there is no point of having a currency.
Economy will remain regardless of the condition, for example, the pandemic.
Why it won't go down? as you see, there were news in the past that tells about stocks plummeting. But the same as bitcoin, they won't be like that for a long time.