Software Philosophy
Software is a non-physical good, and so by nature, I expect it to be free as in freedom and price. This isn't a new philosophy, and it's articulated well by the Free Software Foundation. However, there are pratical limitations to this philosophy because society has been slowly overrun by proprietary software. As a result, one can hardly exist without having to use some proprietary web interface to interact with a corporate entity.
To be clear, software and services are two separate things. I classify software as a program running on my own hardware, and a service is a program running somebody else's hardware. I take no issue with having to pay for a proprietary service. While I would prefer a FOSS (Free and Open Source Software) solution that I could potentially self-host as a fallback, the ownership model at least makes sense and my freedom isn't compromised.
Practical Reasons for FOSS software
Many of the tools that we thought we could rely on broke down, whether it is Apple products, or software that require subscription services, DRM, etc. As an artist you spend time developing a skill, you become a Photoshop illustrator. When your connection to the internet fails and that the software locks up, that skill that you thought was yours was actually entirely owned by someone, and can be taken away.
Outside of the philosophical debate, there are a many pratical reasons for using FOSS products. One is the idea of the ownership of skills articulated by the Hundred Rabbit's artist collective. Most skills rely on a supply chain: a pianist needs piano manufacturers as much as a digital artist needs digital art software. The difference is that software supply chains are especially volatile and subject to change. FOSS is the only guarantee that the time you invest into learning a software can't be taken away. If a FOSS product changes direction and eliminates years of effort and skill a user poured into it, that user has the freedom to continue to use, and even develop, the specific version of the product that empowered them.
For all software markets, it's only a matter of time until the FOSS product becomes the dominant solution, invalidating any proprietary alternatives. This has already happened with Blender taking over the 3D software space. Godot and Krita are also successful projects in their respective fields of game development and digital art. Most of this point is based off of anecdotal evidence, but I believe a good FOSS project guarantees relevance and longevity.
Related to the first point, FOSS products are a good antidote to bitrot. With art related software, there are three components, the project file, the software, and the rendered artifact. While the artifact is the end goal, I also find great value in the project file. Whether it's somebody else's project, or my own from a long time ago, being able to interact with the project file can be educational as well as invaluable if you want to edit or generate the artifact again. This may leave the realm of praticality, but with some elbow grease, it should be possible to open any project file as long as it was created with a FOSS product. This claim is making a lot of assumptions, like having historical code or releases of the software, but I take comfort that project files are less likely to become useless data.