This happens because `distributed < distributed + centralized` nearly always.

For example, git is great, but git plus an (optional) issue tracker has more value, so that's what people use.

Coincidentally (or perhaps causally?), FOSS < FOSS + closed source.

The only way I can see this changing is if the distributed (or free or open-source) benefits of the system fail early and painfully when centralized (or paywalled or close-sourced). I can't think of any such systems off the top of my head.