The companies are not willing to upgrade only if they have old code which works and they do not want to touch it, because upgrading could cause a lot of headaches. But if they are creating a new project, they will choose the most common solution at that time. PHP 7.0 is too new, but there is no reason to support PHP 5.4, which will be obsolete sooner than new framework will be finished. Supporting version 5.6 is reasonable in the long run. As sv3tli0 wrote, upgrading from version 3 to 4 will be almost impossible, so no big deal I think.
