He evidently is permitting this on a tentative basis - if anything comes up that in the slightest contradicts prevailing theory (Hawass & Lerner), it will be quashed quickest. Especially if they determine that the pyramids were built as a complex, not used as tombs, and were rebuilt/repaired during the times of the Old Kingdom.
That was the case with optical thermoluminescence dating (which determines age by measuring electrons released when a stone joint is fractured) in Egypt done by Prof. Ioannis Liritzis in which a few samples added several hundred years to standard dating - making the test subjects far too old to fit and was quickly shut down. This technique is now banned.
As to why the technology was not used earlier - it is a simple matter of getting permission from the idiots mentioned above - a matter of intense negotiations and over many years for the simplest of things.
Some links for those that wish to pursue all things Old Kingdom - books by a real Egyptologist and science historian w/ many unique photos on line:
The Sphinx Mystery
The original Sphinx?
Despite of the admonition to "not trust Ukrainians" at Geological Evidence Shows the Great Sphinx is 800,000 Years Old, it is worth considering that the research done sounds good - based on climatology and geology - furthering West and Schoch's theory of origin.