Companies don't have to go public and list themselves on the stock market, they choose to do this as an easy way to raise capital from investors, providing a financially healthy company capital to rapidly expand, and an unhealthy company a chance to recover. Without the market it would be much more difficult for a chain restaurant to go nationwide seemingly overnight. That void might allow for more localized brands and small businesses, or (and in my opinion more likely) we would have a limited number of mega companies that have been around for generations with pockets large enough to gobble up any competition that starts to present itself. These companies would be unchallengeable without investments from the mega rich. The market levels the playing field in that a new company with promising offerings can gather capital from millions of investors overnight to make a run at today's giants. The unfortunate bit is how the market has been turned into a casino with the players having unfavorable odds, but that's a much larger conversation.