In the US, it's generally very easy to create a "business," which doesn't even need to be a separate legal entity.
I'd guess that a substantial portion of the companies in the denominator have no employees and are just entities for owning a piece of property, or for someone's occasional graphic design work, or whatever. They are legally businesses, but not businesses in the way that we commonly think, such as a local auto shop or retail store.
This is correct, but misleading. In the US, something like > 60% of GDP come from just the US companies in the Fortune 500.
I once worked for a F100 sized healthcare firm that had a separate LLC for each physician it 'employed'. Quotes because the LLC invoiced the parent and then paid the physician, so they were technically an employee of the LLC, but it shielded the company from certain risks and had some tax reasoning and various other mumbo-jumbos
So we get 30 000 or 17 000. Which is entire SnP 500. And probably even every publicly traded company.
For every US Steel, there's a thousand potters throwing vases in their backyard shed.