A "simpler" tool that is easily self-hostable is hard to monetise. For example, I self-host several tools especially frontend such as Ghost, Gatsby, etc.
However, I also have experience of seeing "open core" work as a good business model for several providers. In a complex setup, while the core can be self-hosted for smaller workloads, the need to run production-scale workloads means you need to buy the SaaS license from the provider. Gitlab comes to mind as an example.