Because consciousness itself cannot be explained except through experience ie consciousness (ie first person experience) - not through material phenomena

It’s like explaining music vs hearing music

We can explain music intellectually and physically and mathematically

But hearing it in our awareness is a categorically different activity and it’s experience that has no direct correlation to the physical correlates of its being

The common thought experiment is the color blind researcher experiencing color for the first time(Mary the Colour Scientist https://en.wikipedia.org/wiki/Knowledge_argument)