I,m lead to believe from a very reliable source that the reason the taxiway was never originally extended to the end of runway 26 was that it is going to take a lot of earthworks to build up the ground level as the land falls away rather drastically after the current turning point and it was going to cost more than anyone was prepared to pay for the extra benefit of a full length taxiway.
It was pointed out that when the new dual road was put into the airport a couple of years ago, all that "muck" could have been dumped in the area of the "26" taxiway extension, but that was deemed to much of a good idea by the powers that be.