I think they're simply ploughing all their revenue back into growth through sales/marketing. If they wanted to they could turn down the customer acquisition spend and ride their recurring revenue to a tidy profit.
This can be quite hard to establish, especially for companies that have raised significant capital (Shopify raised $120M+), they can keep that from happening for a long long time.
For companies that have not raised significant capital, if they're able to finance their growth out of their income stream then yes, they can convert to profitable overnight.