Microstrategy is an analytics company that buys bitcoin to pump bitcoin - they own something like 1% of the total supply.
Tether is a cryptocurrency that lets you do tax fraud by being pegged 1:1 to the US dollar, but can be exchanged in-kind for bitcoin so you don't actually trigger a taxable event. It's run by iFinex, a company that also runs the Bitfinex exchange. I'm not really sure that they actually have 120 billion in cash
I have no clue who actually runs these companies tho
They'll have to sell too eventually, not much you can do with Bitcoin.
but if you follow that trail it ends in 'real' money.
say you buy 1kg of coke for 1BTC, that seller then has to sell that Bitcoin for Dollars or whatever their actual currency is. The end effect is the same, crypto goes into exchange, someone else is hopefully willing to hold it for Dollars, price goes down.