Why can't people understand the simple concept of stock buying and selling?
No money was lost, no value was lost. That is a lie.
At the time of selling there is a seller and a buyer. None of that money "disappears".
Not necessarily. If a company takes proceeds from stock and uses that money to invest in, say, infrastructure, that takes resources which are then comsumed (lumber, steel, oil, etc). Sure, the companies that produce these resources get money from that transaction, but there is still money that is locked into those materials. And in cases like China where you literally have shopping malls and entire cities sitting empty there are literally millions of dollars just decaying away. As for the rest of the money, it gets more and more diluted as it passes through the hands of multiple companies and people in the form of wages, payments for goods/services, savings deposits, etc. 1 person with $1,000,000 can have a muhc larger impact on an economy than 1,000,000 people with $1 because he can focus all of that money in one place while the people with $1 can do very little becuase that money might go everywhere.
So basically some of that money does disappear as it is sunk into things whose cost can never be recouped and a lot of the rest can get so spread out and distributed that it loses a lot of the economic power it had that it also might as well not exist.