Companies can be incentived in various ways, including:
- to get to the next round of VC funding
- to be a sustainable profitable business by making more money from customers than they spend, or
- to grow to have a very large number of users and somehow pivot to making money later.
When founding a company, you have a chance to choose how your company will be incentived based on how much risk you are willing to take, the resources you have, the sort of business you are building, the current state of the market, and your model of what will happen in the future.
Source: Sage: Open Source Mathematics Software: RethinkDB, SageMath, Andreessen-Horowitz, Basecamp and Open Source Software
Good article that outlines an open source business model that may work without VC investment.