why doesn't it? some apps can use extensions without the functionality level increase, though in some places the GLSL version increase is really important in others not so much.
Also some developers aren't up to the commitment to the full time task of doing something like geometry or tessellation shaders but have the spare time to add other smaller pieces of functionality and leave the bigger pieces to the full time devs.
Like I've no bandwidth to work on GL4.0 features, but I like to tinker around the edges and look at adding small extensions.
Intel have plans to get to GL4, but they can't control what independent devs work on anyways, you seem unfamiliar with open source.