If it's a few pennies for month how are their operating expenses greater than their revenue? Have you even looked at their public filing or are you just making assumptions?
"Cost of revenue consists primarily of expenses related to hosting Slack and providing ongoing customer support for paid customers. These expenses include employee compensation (including stock-based compensation) and other employee-related expenses for customer experience and technical operations staff, payments to outside service providers, third-party hosting costs, payment processing fees, and amortization expense associated with internally-developed and purchased technology. We expect our cost of revenue to continue to increase in absolute dollar amounts as we grow our business and revenue."
That amortization could be significant; it's likely that they're not spending $5 in hosting and devops alone. It may not be pennies, but it's way less than the cost of a car.
To service their order book, they just need a skeleton crew. And the order book should be the bottom line for the bulk of investors.