Degrees of Openness
Single Source Companies
They're open source, but they're not Open Source.
As a user, these projects provide more value to me than closed-source solutions for all the obvious reasons. As a developer, I understand why choosing such a licensing scheme may make a project commercially viable when it otherwise may not be.
But these are all immediate practical reasons. The long term result of this is a tremendous legal and technological minefield. One of the strongest arguments of the Free software movement was that it makes software free, not humans.
These "open core, single source" projects are not compatible with that vision, they come with all strings attached. The companies putting out these projects will inevitably go under or get acquired. Again, in the short term, as a user I get to keep that software alive for longer than I would have been able to with a closed solution.
However, at that point there can be no forks, no new development in public. The source code itself becomes toxic. Similarities between fragments of these projects and any newly developed software in that space will provide fuel for law suits. Given the vastly larger surface area and distribution of this IP, mega corporations who acquired the rights will have an easier time strangling entire market segments indefinitely.
On balance, I understand why developers are choosing this. They are tired of providing tools that enable billionaires to exist while they themselves are struggling. But in the long term, there will be more problems on the horizon due to this.