Open source also serves as a "defense strategy" for larger companies whose core business does not directly / indirectly depend on commercializing its open source project(s). They in turn serve more like hedges.

For example, Meta with PyTorch in context of the machine learning tooling space. PyTorch is probably strategically important for them as they do not have a cloud business. The other large competing deep learning framework is Tensorflow, designed and open sourced by Google but also owns a cloud business (GCP). They also have in-house AI accelerators like TPUs. Microsoft didn't really have a deep learning framework, but they have ONNX, and is now using ONNXRuntime as an on-ramp to their cloud business (Azure).

If Meta wants to continue doing ML, and all the other cloud players jacked up their prices, that's gonna hurt Meta's operating costs. So it's still "cheap" to have hedged against such a scenario. All these on top of upsides like developer marketing etc.