The article discussed at length that no one understood how the voids would improve structural engineering. I would hazard that they want to think about that more before doing anything.

I’d also imagine that they’d need approval from the Egyptian government and I would also hazard those approvals might not be forthcoming without an abundance of evidence that any sort of exploration would have zero affect on the structure’s integrity:

The coverage I read (National Geographic) described these voids as structural only and without any speculation that they might be hidden chambers.

If that’s the case, it comes as no surprise that they haven’t been explored. No one wants to make a Pyramid tumble down to check out what is basically a structural feature.