Some people think the Egyptian government aims to control archeology so it doesn't find things conflicting with their view of history.

The alternate view is that it's mostly just hopelessly bureaucratic.

An alternative alternative view is that the pyramids are >4000 years old and 20 years is nothing in that context, so waiting a few years for technology to improve to the extent that they can be confident that the archeologists can do an investigation in a less invasive way that doesn't cause damage is time well spent.

The other alternate view is that it's run by an incompetent narcissist (Zahi Hawass, head of the Egyptian Antiquities Department that controls who can do what in the pyramids). Hawass was not particularly supportive of the original ScanPyramids Project results.

'On November 2, 2017, the Egyptologist Zahi Hawass told the New York Times: "They found nothing...This paper offers nothing to Egyptology. Zero."' -- wikipedia.

The result from the ScanPyramids Project that got the most coverage was a strong suggestion that there is a major void (the ScanPyramids Big Void) above the Grand Gallery leading to the King's Chamber (which has not yet been confirmed). They also found weaker evidence that suggested there was a tunnel on the north face behind the chevron blocks. The existence of the ScanPyramids North Face Corridor (referred to in the literature as the SP-NFC) was confirmed in 2023, by inserting an endoscope into a crack between two of the chevron blocks. Zahi Hawass did his best to take credit for the discovery. Nobody took him seriously.

That underground city near Derinkuyu in Turkey is suppose to have 18 levels, the first 8 are open to the public, the other 10 have been waiting for permission since 1963.