Same as any other open-source company, and there are plenty: Terraform(Hashicorp), Docker, RedHat, MongoDB, Elastic, DataBricks, ... . Open source is free, and you sell either additional products on top of it or you offer services like enterprise support and consultancy. The main idea is: if you have an open-source solution that is valuable enough and is catering to big enough market, there will be a lot of value to offer on top of it, and you will be in best position to capture that value and therefore monetize it.
We are not yet developing any products on top of Wasp, first we are focusing on the open-source part of it, but idea is to offer additional products on top of it - we will probably start working on those in a year, once open-source core is stable.