It's not like they have heaps of cash, they'd do work for their clients or supply their customers, issuing the bill for hours worked/items delivered at the end of the month, and the bill might have a term like "payable within 30 days". So the companies would have to have some cash to pay their employees in the month where they're waiting for their customers' money.

In fact IIRC this was the big worry during the 2008 crash, if the banks were worried companies would grind to a halt and not pay their suppliers, why should the bank give out loans to said suppliers...