It's continually testing the strength of SHA256. If you can find a way to even partially crack it, you win money. Edit: Also, way more hashes are happening all the time now, increasing the chance that someone finds a collision if it were possible.
Cracking hashes would imply that they're taking pre-existing hashes and reversing them to find the input.
So why'd you bring it up?
Cracking sha256 hashes implies trying to reverse a specific hash. There are literally thousands (millions?) of potential inputs that hash to a valid bitcoin mining block output. It's basically a race to find the first one matching the rules of the current block difficulty. The goal isn't to produce any one specific input/hash pair.
Hash collision should always be about finding matching content for a hash.
Be a bitch to search. But damn would we know the topography of the function space.
...I'll see myself out.