Why is data stored on a flash disk irretrievable if the memory chip is cracked?
The data may well still be there, the problem is that there is no (reasonable) way to get an electrical signal into or out of the data cells.  When you crack a chip you are cracking wires.  The minimum feature size in many chips made these days is around 20nm=200 Angstroms.  I suppose that if you (a) had an electron microscope, (b) knew exactly how the manufacturer had laid out the chip (what every wire means, and what signals need to be sent where to get the data), and (c) had some kind of electron microscope based soldering iron or micro-manipulator with a tip just a few atoms wide, you could laboriously and painstakingly repair all those broken connections.

But, while data recovery companies (the super duper ones) might have electron microscopes, I doubt they have either (b) any access to the manufacturer's layout or (c) a micromanipulator that could actually be used to do the repair.  Also, we're talking about potentially needing to repair thousands of connections, so even if someone were able to do it, they'd probably charge tens or hundreds of thousands of dollars.