This is because they have to invest heavily upfront to acquire the customer, but recover the profits from that investment over a long period of time. The faster the business decides to grow, the worse the losses become. Many investors/board members have a problem understanding this, and want to hit the brakes at precisely the moment when they should be hitting the accelerator.
In many SaaS businesses, this also translates into a cash flow problem, as they may only be able to get the customer to pay them month by month.