BSD jails weren't widely adopted because the BSDs themselves weren't widely adopted by the time the industry got to the point where something like Docker was increasingly seen as necessary. I remember being involved in one project that had to decide this exact question in the very early days of Docker - jails were much more stable back then, but customers wanted Linux containers, not "sufficiently Linux-like".

I think the GP's point is that alternatives can easily spring up when the main feature-set/value is in the kernel rather than the glue code.