User asks for an explanation of why quantum computing companies are listed on the stock exchange

The stock market is just gambling. But it's not betting on a certain company's well-being, it's whether high frequency trading algos and market maker loophole abuse will make your portfolio improve or not. If you foresaw the dude saying the thing and got some order set up to catch it in time you might even get a trade on the lit market, but most trading happens somewhere else at different prices and at times you're not allowed to participate.